#include "bits/stdc++.h"
#define rep(i, a, n) for (auto i = a; i <= (n); ++i)
#define revrep(i, a, n) for (auto i = n; i >= (a); --i)
#define all(a) a.begin(), a.end()
#define sz(a) (int)(a).size()
using namespace std;

using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;


int main() {
	ios::sync_with_stdio(0); cin.tie(0);

	int n, m; 
	while (cin >> n >> m) {
		string s; cin >> s;
		vvi g(n);
		rep(i, 1, m) {
			int x, y; cin >> x >> y;
			x--, y--;
			g[x].push_back(y);
			g[y].push_back(x);
		}
		vi cnt(n);
		rep(i, 0, n - 1) for (auto j: g[i]) if (s[j] != s[i]) cnt[i]++;
		ll ans = 0;
		rep(now, 0, n - 1) if (s[now] == 'b') {
			for (auto v: g[now]) if (s[v] == 'o') {
				ans += 1ll * (cnt[now] - 1) * (cnt[v] - 1);
			}
		}
		printf("%lld\n", ans);
	}
	return 0;
}