from collections import defaultdict
from sys import stdin

def main():
    N = int(input())
    S = input()

    txt = defaultdict(list)
    for i, s in enumerate(S):
        txt[s].append(i)

    ans = 0
    for i in txt['U']:
        for n in range(1, 2500):
            m = i + n
            g = m + n
            if g >= N:
                break
            else:
                if S[m] == 'M' and S[g] == 'G':
                    ans += 1
    print(ans)

input = lambda: stdin.readline().rstrip()
main()