#include<stdio.h>
int v[10000],n,t,fr[26];
void readsolve()
{
	FILE*f=fopen("litere.in","r");
	fscanf(f,"%d",&n);
	int i=0,j;
	char var;
	fscanf(f,"%c",&var);
	for(;i<n;++i)
	{
		fscanf(f,"%c",&var);
		v[i]=var-97;
		for(j=v[i]+1;j<26;++j)
			t+=fr[j];
		++fr[v[i]];
	}
	fclose(f);
}
int main()
{
	readsolve();
	/*for(i=0;i<n-1;++i)
	{
		for(j=i+1;j<n;++j)
			if(v[i]>v[j])++t;
	}*/
	FILE*g=fopen("litere.out","w");
	fprintf(g,"%d",t);
	fclose(g);
	return 0;
}