N =int(input())
S =[i for i in input()]
dic = {"U":[],"M":[],"G":[]}
for i,str in enumerate(S):
    dic[str].append(i)
ans = 0
for j in dic["M"]:
    for i in dic["U"]:
        if i > j:
            break
        if 2*j - i in dic["G"]:
            ans += 1
print(ans)