#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 2e5 + 10;
char c[N];
vector<int> vt[N];
int b[N];
int main()
{
    int n, m;
    while (scanf("%d%d", &n, &m) != EOF)
    {
        vector<int> bb;
        for (int i = 1; i <= n; i++)
        {
            vt[i].clear();
            cin >> c[i];
            if (c[i] == 'b')
                bb.push_back(i);
        }
        for (int i = 1; i <= m; i++)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            if (c[u] == 'b' && c[v] == 'o')
            {
                vt[u].push_back(v);
                vt[v].push_back(u);
            }
            else if (c[u] == 'o' && c[v] == 'b')
            {
                vt[u].push_back(v);
                vt[v].push_back(u);
            }
        }
        ll ans = 0;
        for (int i = 0; i < bb.size(); i++)
        {
            b[bb[i]] = vt[bb[i]].size();
        }
        for (int i = 1; i <= n; i++)
        {
            if (c[i] == 'o')
            {
                for (int j = 0; j < vt[i].size(); j++) // c[vt[j]]=b;
                {
                    int v = vt[i][j]; // i-v
                    ans += (vt[i].size() - 1) * (b[v] - 1);
                }
            }
        }
        printf("%lld\n", ans);
    }
    return 0;
}