#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("litere.in");
ofstream fout ("litere.out");
int v[10001],f[26];
int main()
{int n,s=0;
fin>>n;
char c;
for(int i=1;i<=n;i++)
{
    fin>>c;
    c=c-'a';
    v[i]=c;
}
f[v[0]]++;
for(int i=1;i<=n;i++)
{
    for(int j=v[i]+1;j<26;j++)
    s=s+f[j];
    f[v[i]]++;
}
fout<<s;
    return 0;
}