#include<string.h>
#include<vector>
#include<iostream>
#include<assert.h>

using namespace std;
#define int long long 

const int N = 2e5+10;

int bb[N], oo[N];
char ch[N];
vector<int > son[N];
int n, m;

void work(){
    
    for(int i = 0; i <= n + 2; i ++){
        son[i].clear();
        bb[i] = oo[i] = 0;
    }

    cin >> (ch + 1);
    for(int a, b, i = 1; i <= m; i ++){
        cin >> a >> b;
        son[a].push_back(b);
        son[b].push_back(a);
    }

    for(int x = 1; x <= n; x ++){
        for(int t : son[x]){
            if(ch[t] == 'o'){
                oo[x] ++;
            }
            else{
                bb[x] ++;
            }
        }
    }

    int seele = 0;
    for(int f = 1; f <= n; f ++){
        if(ch[f] == 'o'){
            for(int t : son[f]){
                if(ch[t] == 'b'){
                    seele += (bb[f] - 1) * (oo[t] - 1);
                }
            }
        }
    }

    cout << seele << '\n';

}


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

    int __ = 1;
//    cin >> __;

    while(cin >> n >> m){
        work();
    }
}

/*


3 2
1 2 1
2 3 1
1 3 3
1
2
5 1
1
4
5 4
1
4
5 1

*/