#include <bits/stdc++.h>

using namespace std;
ifstream in ("litere.in");
ofstream out ("litere.out");
char s[10002];
int n,i,j,k;
int main()
{
    in>>n>>s;
    int ok=1;
    while(ok)
    {
        ok=0;
        for(i=0; i<n-1; i++)
            if(s[i]>s[i+1])
                swap(s[i],s[i+1]),k++,ok=1;
    }
    out<<k;
    return 0;
}