#include<stdio.h>
#include<stdlib.h>

#define STR_LENGTH 5001

int main(void){
  char str[STR_LENGTH];
  unsigned int len = 0;
  unsigned int ans = 0;
  int k = 0;

  fgets(str, sizeof(str), stdin);
  len = (unsigned int) atoi(str);

  fgets(str, sizeof(str), stdin);

  for(int i=0; str[i] != '\0'; i++){
    if('U' == str[i]){
      for(int j=i+1; str[j] != '\0'; j++){
        if('M' == str[j]){
          k = 2 * j - i;
          if((k <= len) && ('G' == str[k])){
            ans++;
          }
        }
      }
    }
  }

  printf("%d\n", ans);
  return 0;
}