#include<stdio.h>
#include<string.h>
FILE*f=fopen("litere.in","r");
FILE*g=fopen("litere.out","w");
char v[10003];
long a[29];
long long sol;
int n;
void read()
	{
	char c;
	fscanf(f,"%d\n",&n);
	for(int i=1;i<=n;++i)
		{
		fscanf(f,"%c",&v[i]);
		}
	}
void solve()
	{
	int i,j;
	for(i=1;i<=n;++i)
		{
		a[v[i]-96]++;
		for(j=v[i]-96+1;j<=26;++j) sol+=a[j];
		}
	fprintf(g,"%lld",sol);
	}
int main() {read();solve();return 0;}