#include<fstream>
using namespace std;ifstream f("litere.in");ofstream g("litere.out");int n,i,r,v[257],j;char q;int main(){f>>n;for(i=1;i<=n;i++){f>>q;v[q]++;for(j=q+1;j<='z';j++)r=r+v[j];}g<<r;return 0;}