#include <cstdio>
using namespace std;

int v[1000000];

int main()
{
    freopen("litere.in","r",stdin);
    freopen("litere.out","w",stdout);

    int i, j, k, n;
    char x;

    k = 0;

    scanf("%d%*c",&n);

    for( i = 1; i <= n; ++i ){
        scanf("%c",&x);
        v[x-'a'+1]++;
        for( j = x - 96; j < 26; ++j ) k += v[j+1];
    }

    printf("%d",k);




    return 0;
}