package main

import . "fmt"

func main() {
	var n int
	var s string
	Scan(&n,&s)
	b:=[]byte(s)
	us:=[]int{}
	ms:=[]int{}
	for i,c:=range b {
		if c=='U' {
			us=append(us,i)
		}
		if c=='M'&&len(us)>0 {
			ms=append(ms,i)
		}
	}
	if len(us)==0||len(ms)==0||len(us)+len(ms)==n{
		Println(0)
		return
	}
	var ans int64
	for _,i:=range us {
		for len(ms)>0&&ms[0]<i {
			ms=ms[1:]
		}
		for _,j:=range ms {
			k:=j+j-i
			if k<n&&b[k]=='G' {
				ans++
			}
		}
	}
	Println(ans)
}