#include <cstdio>
#include <algorithm>
using namespace std;

int v[10001];

int main()
{

    freopen("litere.in","r",stdin);
    freopen("litere.out","w",stdout);
    char x ;
    int n, i, j, s= 0;

    scanf("%d%*c",&n);
    for( i = 1; i <= n; ++i ){
        scanf("%c",&x);
        v[i] = x - 'A';
    }

    for( i = 1; i <= n; ++i ){
        if( v[i] < v[i-1] ){
            //swap( v[i], v[i-1] );
            //s++;
            for( j = i; v[j] < v[j-1]; --j ) if( v[j] < v[j-1] ){
                    swap( v[j], v[j-1] );
                    s++;
            }
        }
    }
    printf("\n%d",s);


    return 0;
}