#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
#include <iostream>
#include <cmath>
using namespace std;
const int maxn = 2e5 + 10;
struct Edge{
	int to,next;
}e[maxn << 1];
int head[maxn],tot;
int cnto[maxn],cntb[maxn];
int n,m;
string c;

void addedge(int u,int v)
{
	e[++tot] = Edge({v,head[u]});
	head[u] = tot;
}

int main() {
	ios::sync_with_stdio( 0 );
	cin.tie( 0 );
	cout.tie( 0 );
	while ( cin >> n >> m ) {
		cin >> c;
		c = " " + c;
		for ( int i = 1; i <= n; i ++ ) {
			cnto[i] = cntb[i] = 0;
			head[i] = - 1;
		}
		tot = 0;
		for ( int i = 1; i <= m; i ++ ) {
			int u, v;
			cin >> u >> v;
			if ( c[u] == 'o' ) {
				cnto[v]++;
			} else cntb[v] ++;
			if ( c[v] == 'o' ) {
				cnto[u] ++;
			} else cntb[u] ++;
			addedge( u, v );
			addedge( v, u );
		}
		long long ans = 0;
		for ( int i = 1; i <= n; i ++ ) {
			for ( int j = head[i]; ~ j; j = e[j].next ) {
				int to = e[j].to;
				if ( c[i] == 'o' && c[to] == 'b' ) {
					ans += 1ll * (cntb[i] - 1) * (cnto[to] - 1);
				}
			}
		}
		cout << ans << "\n";
	}
	return 0;
}