#include <cstdio>
char a[10005];
int b[10005];
int main () {
	int n,i,c=0,aux;
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	scanf("%d",&n);
	for(i=1;i<=n+1;++i)scanf("%c",&a[i]);
	for(i=1;i<=n+1;++i)b[i]=a[i]-'a';
	for(i=2;i<=n+1;++i){
		if(b[i]<b[i-1]){
			aux=b[i];
			b[i]=b[i-1];
			b[i-1]=aux;
			++c;
			i=2;
		}
	}
	printf("%d",c);
	
	return 0;
}