#include <bits/stdc++.h>

using std::ios;
using std::cin;
using std::cout;
typedef long long ll;
const int N = 2e5 + 5;
int n, m, degb[N], dego[N], pu[N], pv[N];
char s[N]; ll ans;

int main()
{
//   freopen("a.in", "r", stdin);

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    while (cin >> n >> m)
    {
    cin >> s;
    for (int i = 1, u, v; i <= m; ++i)
    {
        cin >> u >> v;
        if (s[v - 1] == 'b')
            ++degb[u];
        else
            ++dego[u];
        if (s[u - 1] == 'b')
            ++degb[v];
        else
            ++dego[v];
        pu[i] = u, pv[i] = v;
    }
    ans = 0;
    for (int i = 1; i <= m; ++i)
    {
        if (s[pu[i] - 1] == 'b')
            std::swap(pu[i], pv[i]);
        if (s[pu[i] - 1] == 'o' && s[pv[i] - 1] == 'b')
            ans += 1ll * (degb[pu[i]] - 1) * (dego[pv[i]] - 1);
    }
    cout << ans << '\n';
    for (int i = 1; i <= n; ++i)
        degb[i] = dego[i] = 0;
    }

    return 0;
}