import sequtils
template `max=`*(x,y) = x = max(x,y)
template `min=`*(x,y) = x = min(x,y)
proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" ,discardable.}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': return
    result = 10 * result + k.ord - '0'.ord

let n = scan()
let S = stdin.readLine()
var U = newSeq[int]()
var ans = 0
for i in 0..<n:
  if S[i] == 'G' : continue
  if S[i] == 'U':
    U &= i
    continue
  # M
  for ui in (U.len-1).countdown(0):
    let gi = i - U[ui] + i
    if gi >= n : break
    if S[gi] == 'G' : ans += 1
echo ans