#include <iostream>

char S[5001];
short n, i, j;
int res = 0;

int main(void){
  scanf("%hd\n%s",&n, S);
  for(i = 0; i <= n - 1; i++){
    if(S[i] == 'U'){
      const short edge = (n-1-i) / 2;
      for(j = 1; j <= edge; j++){
        if(S[i+j] == 'M' and S[i+j*2] == 'G') res++;
      }
    }
  }
  printf("%d\n", res);
  return 0;
}