import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
S=input()
U=[]
ans=0
for i in range(n):
  if S[i]=="U":
    U.append(i)
  elif S[i]=="M":
    for u in U:
      if 2*i-u<n and S[2*i-u]=="G":
        ans+=1
print(ans)