#include<stdio.h>
char c[10010];
int N,s=0;
int nr(int x, char y)
{
    int rez=0;
    for(int i=1;i<=x;++i)
        if(c[i]>y)
            ++rez;
    return rez;
}
int main()
{
    freopen("litere.in","r",stdin);
    freopen("litere.out","w",stdout);
    scanf("%d\n",&N);
    for(int i=1;i<=N;++i)
    {
        scanf("%c",&c[i]);
        if(i>1)
            s=s+nr(i-1,c[i]);
    }
    printf("%d",s);
    return 0;
}