#include<stdio.h>

char S[10000];
int N;
int nr = 0;

int main()
{
	int gata;
	char c;
	FILE *f = fopen("litere.in","r");
	FILE *g = fopen("litere.out","w");
	
	fscanf(f,"%d %s",&N,S);
	do
	{
		gata = 1;
		for(int i=0;i<N-1;i++)
			if(S[i]>S[i+1])
			{
				c = S[i];
				S[i] = S[i+1];
				S[i+1] = c;
				nr ++;
				gata = 0;
			}
	} while(!gata);
	fprintf(g,"%d",nr);
	
	fclose(g);
	fclose(f);
}