#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
const int Nmax=10005;
int A[Nmax],N,DP[Nmax],S;

void Read()
{
    fin>>N;
    for(int i=1;i<=N;++i)
    {
        char x;
        fin>>x;
        A[i]=x-96;
    }
}


void Solve()
{
    for(int i=1;i<=N;++i)
    {
        for(int j=i-1;j>=1;--j)
        {
            if(A[j]>A[i])
            {
                DP[i]++;
            }
        }
    }
    for(int i=1;i<=N;++i)
    {
        S=S+DP[i];
    }
    fout<<S<<"\n";
}

int main()
{
    Read();
 Solve();

    return 0;
}