#include<cstdio>

#include<iostream>

#define ll long long

using​namespace​std;

int​n, a[500005], nxt[500005][2];

int​lst[2];

char​c;

ll ans;

ll clac(​int​L, ​int​R) {

​if​(R - L + 1 < 3) ​return​0;

​return​1ll * (R - L + 1 - 3 + 1) * (R - L + 1 - 3 + 1 + 1) / 2;

}

int​main() {

​scanf​(​"%d"​, &n);

​for​(​int​i = 1; i <= n; i++) {

​c = ​getchar​(); ​while​(c != ​'G'​&& c != ​'H'​) c = ​getchar​();

​if​(c == ​'G'​) a[i] = 1;

​}

​lst[0] = lst[1] = n + 1; nxt[n + 1][0] = nxt[n + 1][1] = n + 1;

​for​(​int​i = n; i >= 1; i--) {

​nxt[i][0] = lst[0]; nxt[i][1] = lst[1];

​lst[a[i]] = i;

​}

​ans = clac(1, n);

​for​(​int​i = 1; i <= n; i++) {

​int​L;

​if​(a[i]) {

​L = max(nxt[i][1], nxt[nxt[i][0]][0]);

​}

​else​{

​L = max(nxt[i][0], nxt[nxt[i][1]][1]);

​}

​if​(L - i + 1 < 3) L = i + 2 - 1;

​ans -= max(0, n - L + 1);

​int​R = nxt[i][a[i] ^ 1] - 1;

​if​(R - i + 1 >= 3) ans -= R - i + 1 - 3 + 1;

​}

​printf​(​"%lld"​, ans);

​return​0;

}