#include<stdio.h>
#define N 10005
int n, suma=0, i, j, w[N];
char v[N];
const char in[]= "litere.in";
const char out[]= "litere.out";

int main()
{
	freopen(in,"r",stdin);
	freopen(out,"w",stdout);
	scanf("%d",&n);
	scanf("%s",v);
	for(i=0;i<n;++i)
		for(j=i-1;j>=0;--j)
			if(v[j]>v[i])++suma;
			printf("%d\n",suma);
return 0;
}