#include <cstdio>
void swap(char &a,char &b){
	char c;
	c=a;
	a=b;
	b=c;
}
char cuv[10005];
int main(){
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	int n,i,k=0; bool schimb=0;
	scanf("%d",&n);
	scanf("%s",cuv);
	while(!schimb){
		schimb=1;
		for(i=0;i<n-1;i++)
			if(cuv[i]>cuv[i+1]){
				schimb=0;
				swap(cuv[i],cuv[i+1]);
				++k;
	//			printf("%c %c\n",cuv[i],cuv[i+1]);
			}
	}
//	printf("%s \n",cuv);
	printf("%d",k);
}