#include<stdio.h>
FILE *fin, *fout;
int n,p,ip,nr,i;
char s[12000],ch;

int main(){

	fin=fopen("litere.in","r");
	fout=fopen("litere.out","w");
	
	fscanf(fin,"%d\n",&n);
	fgets(s,12000,fin);
	
	p=0;ip=-1;
	
	while(p<n-1){
		p++;
		if(s[p]<s[p-1] && p>=1){
			if(ip==-1){ ip=p; }
			ch=s[p];
			s[p]=s[p-1];
			s[p-1]=ch;
			nr++;
			
			p=p-2;
		}
		else{
			if(ip!=-1){
				p=ip;
				ip=-1;
			}
		}
		
	}
	
	/*for(i=0;i<n;i++){
		fprintf(fout,"%c",s[i]);
	}
	*/
	fprintf(fout,"%d",nr);
	
	fclose(fout);
	fclose(fin);
	
return 0;
}