def main(): N = int(input()) S = input() u = S.find('U')+1 cnt = 0 while u: m = S.find('M',u)+1 while m: g = m*2 - u if g <= N: if S[g-1] =='G': cnt +=1 m = S.find('M',m)+1 u = S.find('U',u)+1 print(cnt) main()