#include <bits/stdc++.h>
using namespace std;
// #define int long long
signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int n, m;
    while (cin >> n >> m) {
        string s; cin >> s;
        vector<vector<int>> vec(n + 1);
        vector<int> vis(n + 1), cnt(n + 1);
        for (int i = 1; i <= m; i++) {
            int u, v; cin >> u >> v;
            vec[u].push_back(v);
            vec[v].push_back(u);
        }
        s = ' ' + s;
        int ans = 0;
        for (int i = 1; i <= n; i++) {
            if (s[i] == 'b') {
                for (int j = 0; j < vec[i].size(); j++) {
                    int y = vec[i][j];
                    if (s[y] == 'o') cnt[i]++;
                }
            }
            else {
                for (int j = 0; j < vec[i].size(); j++) {
                    int y = vec[i][j];
                    if (s[y] == 'b') cnt[i]++;
                }
            }
        }
        for (int i = 1; i <= n; i++) {
            if (s[i] == 'o') {
                for (int j = 0; j < vec[i].size(); j++) {
                    int y = vec[i][j];
                    if (s[y] == 'b') {
                        ans += (cnt[i] - 1) * (cnt[y] - 1);
                    }
                }
            }
        }
        cout << ans << '\n';
    }
    return 0;
}