#include<fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,x,y,i,j;
char S[10005];
int main ()
{
    fin>>n;
    fin>>S;
    x=0;
    for(i=1;i<n;i++)
    {
        y=x;
        for(j=0;j<i;j++)
        if(S[j]>S[i])
        y++;
        x=y;
    }
    fout<<y;
}