#include<cstdio>
using namespace std;
char s[10001];
int main(){
    freopen ("litere.in","r",stdin);
    freopen ("litere.out","w",stdout);
    int n,i,j,k=0;
    scanf ("%d\n",&n);
    scanf ("%s",&s);
    for(i=1;i<n;i++)
        for(j=0;j<i;j++)
            if (s[j]>s[i]) k++;
    printf ("%d",k);
    return 0;
}