#include<stdio.h>
#include<string.h>
FILE*f=fopen("litere.in","r");
FILE*g=fopen("litere.out","w");
char v[10003];
long long sol;
int n;
void read()
	{
	fscanf(f,"%d\n%s",&n,v);
	}
void bubble()
	{
	int i,j,ok;
        char aux;
	for(i=0;i<n-1;++i)
	{
		j=i;
		while(j>=0&&v[j+1]<v[j])
			{
			sol++; aux=v[j+1]; v[j+1]=v[j]; v[j]=aux;
			j--;
			}

		}



	fprintf(g,"%lld",sol);}
int main()
	{
	read();
	bubble();
	return 0;
	}