# python template for atcoder1
import sys
sys.setrecursionlimit(10**9)
input = sys.stdin.readline

N = int(input())
S = input()[:-1]

U = []
ans = 0
for i, c in enumerate(S):
    if c == "U":
        U.append(i)
    elif c == "M":
        for u in U:
            if 2*i-u < N and S[i+i-u] == "G":
                ans += 1
print(ans)