#include<stdio.h>
FILE *fin=fopen("litere.in","r");
FILE *fout=fopen("litere.out","w");
char v[10001],x;
int sw,aux,i,k,n;
int main(){
	fscanf(fin,"%d",&n);
	fscanf(fin,"%c",&x);
	for(i=1;i<=n;i++)
		fscanf(fin,"%c",&v[i]);
	k=0;
	do{
		sw=0;
		for(i=1;i<n;i++)
			if(v[i]>v[i+1]){
				aux=v[i];
				v[i]=v[i+1];
				v[i+1]=aux;
				sw=1;
				k++;
			}
	}while(sw);
	fprintf(fout,"%d",k);
	fclose(fin);
	fclose(fout);
	return 0;
}