import collections
import itertools


def main():
    n = int(input())
    s = input()

    d = collections.defaultdict(list)
    for i, c in enumerate(s, 1):
        d[c].append(i)

    ans = 0
    for i, j in itertools.product(d['U'], d['M']):
        if i > j:
            continue
        k = 2 * j - i
        if j < k <= n and k in d['G']:
            ans += 1
    print(ans)


if __name__ == "__main__":
    main()