#include <bits/stdc++.h>

//std::ifstream in("carici.in");
std::ifstream in ("litere.in");
std::ofstream out("litere.out");

using namespace std;

int V['z'+1];
int K;
char S;
long long Answer;
int main()
{
   in >> K;
   while( in >> S )
   {
       V[(int)S]++;
       for ( int O = S + 1 ; O <= 'z' ; ++O)
        Answer += V[O];
   }
   out << Answer;
}