#include<bits/stdc++.h>
using namespace std;
#define intmx INT_MAX
#define in ifstream f
#define out ofstream g
#define ll long long
#define ull unsigned long long
int ans=0;
char s[10000];
int n;
int main(){
    in("litere.in");
    out("litere.out");
    f>>n;
    f>>s;
    int srt;
    do{
        srt=1;
        for(int i=0;i<strlen(s)-1;++i){
            if(s[i]>s[i+1]){
                ans++;
                srt=0;
                swap(s[i],s[i+1]);
            }
        }
    }while(!srt);
    g<<ans;
    f.close();
    g.close();
    return 0;
}