bool operator<(const Num &a, const Num &b) {
if (a.size() != b.size()) {
return a.size() < b.size();
} else {
return a.repr < b.repr;
}
}
const Num operator+(const Num &a, const Num &b) {
string res;
int len = max(a.size(), b.size());
string x = a.repr;
string y = b.repr;
reverse(x.begin(), x.end());
reverse(y.begin(), y.end());
x += string(len-x.size(), '0');
y += string(len-y.size(), '0');
int c = 0;
for (int i=0; i<len; ++i) {
int d = val[x[i]] + val[y[i]] + c;
res += dig[d%36];
c = (d>=36);
}
if (c) {
res += '1';
}
reverse(res.begin(), res.end());
return Num(res);
}