int get_dist(const II &st, const II &ed) {
if (st == ed) {
return -1;
}
int d[64][64];
memset(d, -1, sizeof(d));
II dirs[4] = {II(-1,0),II(1,0),II(0,-1),II(0,1)};
IIVec q;
d[st.second][st.first] = 0;
q.push_back(st);
while (q.size() > 0) {
IIVec nq;
int i, j;
for (i = 0; i < (int)q.size(); ++i) {
const II ¤t = q[i];
if (current == ed) {
return d[current.second][current.first];
}
for (j = 0; j < 4; ++j) {
int x = current.first + dirs[j].first;
int y = current.second + dirs[j].second;
if (x >= 0 && x < W && y >= 0 && y < H &&
d[y][x] < 0 && fld[y][x] != '#') {
nq.push_back(II(x, y));
d[y][x] = d[current.second][current.first] + 1;
}
}
}
q = nq;
}
return -1;
}
int solve(void) {
IIVec q;
q.push_back(II(sx, sy));
for (int t = 1; q.size() > 0; ++t) {
IIVec next;
for (int i = 0; i < (int)q.size(); ++i) {
const int dx[4] = { -1, 0, 1, 0 };
const int dy[4] = { 0, -1, 0, 1 };
for (int d = 0; d < 4; ++d) {
int x = q[i].first + dx[d], y = q[i].second + dy[d];
if (x >= 0 && y >= 0 && x < W && y < H && ((1 << (t % 4)) & z[y][x]) == 0) {
if (x == gx && y == gy) {
return t;
}
if (!vis[t % 4][y][x] && maze[y][x] == '.') {
vis[t % 4][y][x] = 1;
next.push_back(II(x, y));
}
}
}
}
q = next;
}
return -1;
}
int maxSongs(vector <int> duration, vector <int> tone, int T) {
IIVec v;
int N = (int)tone.size();
int i, j, k;
for (i = 0; i < N; ++i) {
v.push_back(II(tone[i], duration[i]));
}
sort(v.begin(), v.end());
#define INF 0x3f3f3f3f
int dp[64][64] = {};
memset(dp, 0x3f, sizeof(dp));
for (i = 0; i < N; ++i) {
for (j = 0; j < i; ++j) {
for (k = 1; k <= i; ++k) {
dp[i][k+1] = min(dp[i][k+1], dp[j][k] + v[i].first-v[j].first + v[i].second);
}
}
dp[i][1] = v[i].second;
}
int ans = 0;
for (k = 1; k <= N; ++k) {
for (i = 0; i < N; ++i) {
if (dp[i][k] <= T) {
ans = k;
}
}
}
return ans;
}
int maxSongs(vector <int> duration, vector <int> tone, int T) {
int ans = 0;
IIVec v;
for (int i = 0; i < (int)tone.size(); ++i) {
v.push_back(II(tone[i], duration[i]));
}
sort(v.begin(), v.end());
int dp[64][64];
memset(dp, 0x3f, sizeof(dp));
for (int i = 0; i < (int)v.size(); ++i) {
for (int j = 0; j < i; ++j) {
for (int k = 1; k <= i; ++k) {
dp[i][k + 1] = min(dp[i][k + 1], dp[j][k] + abs(v[i].first - v[j].first) + v[i].second);
if (dp[i][k + 1] <= T) {
ans = max(ans, k + 1);
}
}
}
dp[i][1] = v[i].second;
if (v[i].second <= T) {
ans = max(ans, 1);
}
}
return ans;
}
double maxExpectation(int M, vector <int> day, vector <int> win, vector <int> gain) {
Max = M;
IIVec Days;
int i;
for (i = 0; i < (int)day.size(); ++i) {
if (win[i] > 0 && gain[i] > 0) {
Days.push_back(II(day[i], i));
}
}
sort(Days.begin(), Days.end());
_day.clear();
_win.clear();
_gain.clear();
memset(memo, 0, sizeof(memo));
for (i = 0; i < (int)Days.size(); ++i) {
_day.push_back(Days[i].first);
_win.push_back(win[Days[i].second] * 0.01);
_gain.push_back(gain[Days[i].second]);
}
if (Days.size() <= 0 || M <= _day[0]) {
return M;
}
return rec(0, M - _day[0]);
}
vector <int> minimalDifference(vector <int> h) {
int N = (int)h.size();
IIVec v;
for (int i = 0; i < N; ++i) {
v.push_back(II(h[i], i));
}
sort(v.begin(), v.end());
vector <int> ans(N);
int l = 0, r = N - 1;
for (int i = 0; i < N; ++i) {
if (i % 2) {
ans[r--] = v[i].second;
} else {
ans[l++] = v[i].second;
}
}
return ans;
}
int main(int argc, char *argv[])
{
IIVec v;
int N;
cin >> N;
for (int i = 0; i < N; ++i) {
int a;
cin >> a;
v.push_back(II(a, i));
}
sort(v.begin(), v.end());
int ans = 0;
for (int i = 0; i < N; ++i) {
ans += (i % 2) != (v[i].second % 2);
}
cout << ans / 2 << endl;
return 0;
}
vector <int> construct(vector <int> x) {
IIVec v;
for (int i = 0; i != x.size(); ++i) {
v.push_back(II(x[i], i));
}
sort(v.begin(), v.end());
vector <int> ans;
for (int i = 0; i != v.size(); ++i) {
if (v[i].first > (i + 1)) {
ans.resize(1);
ans[0] = -1;
break;
}
for (int j = 0; j < (v[i].first - 1); ++j) {
ans.push_back(v[i].second);
ans.push_back(v[j].second);
}
}
return ans;
}