void dj(int p,int *d,bool *s,pq q){
for (int i=1;i<=n;i++)
d[i]=inf;
d[p]=0;
q.push(make_pair(0,p));
// wu s[1]!!
for (int z=1;z<=n;z++){
/*pii tmp=q.top();q.pop();//pop!
while (!q.empty() && s[tmp.se]){
tmp=q.top();q.pop();
}
if (s[tmp.se])//not q.empty()!!!!!!!!!!!!!!!!!!!!!!! abnormal stop!*/
if (q.empty()) break;//!!!!!!!!!!!!!!
pii tmp=q.top();q.pop();
while (!q.empty() && s[tmp.se]){//!!!!!!!
tmp=q.top();q.pop();
}
int x=tmp.se;
if (s[x]) break;
s[x]=true;
for (int i=hd[x];i;i=e[i].ne){
int y=e[i].v;//y not j!
if (!s[y] && d[x]+e[i].w<d[y]){//!s!
d[y]=d[x]+e[i].w;
q.push(make_pair(d[y],y));
}
}
}
}
void dj(int p,int * d,int * s,pq q){
for(int i = 1;i<=n;++i) d[i] = INF;
d[p] = 0;q.push(MP(0,p));
for(int z = 1;z<=n;++z){
if(q.empty()) break;
pii tmp = q.top();q.pop();
while(!q.empty() && s[tmp.Y]) tmp = q.top(),q.pop();
int x = tmp.Y;
if(s[x]) break;
s[x] = 1;
for(int i = hd[x];i;i=e[i].ne){
int y = e[i].v;
if(!s[y] && d[y] > d[x]+e[i].w)d[y] = d[x]+e[i].w,q.push(MP(d[y],y));
}
}
}
int main(void)
{
long long num;
cin >> num;
long long sum = 0;
for (long long i = 0; i < num; i++) {
long long temp;
cin >> temp;
small.push(-temp);
big.push(temp);
sum += temp;
}
if (sum%num) {
cout << "Impossible";
return 0;
}
long long count = 0;
for (; ; ) {
//cout << big.top() << " " << -small.top() << endl;
if (-small.top() > big.top()) {
cout << "Impossible";
break;
}
if (big.top()-1 == -small.top()) {
cout << "Impossible";
break;
}
long long x = big.top();
if (big.top() == -small.top()) {
cout << count << endl;
break;
}
big.pop();
big.push(x-1);
long long y = small.top();
small.pop();
small.push(y-1);
count++;
}
}