import java.util.*;

public class buyingjerseys_ls {
    static ArrayList<HashMap<Integer, Integer>> graph;
    static ArrayList<Integer> visited;
    static int timer;
    static int T;

    static boolean dfs(int i) {
        if (i == T) return true;
        if (visited.get(i) == timer) return false;
        visited.set(i, timer);

        for (var entry : graph.get(i).entrySet()) {
            int ni = entry.getKey();
            int w = entry.getValue();

            if (w>0 && dfs(ni)) {
                graph.get(i).put(ni, w-1);
                graph.get(ni).put(i, 1+graph.get(ni).getOrDefault(i, 0));
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int n = in.nextInt();
        int m = in.nextInt();


        ArrayList<Integer> rivals = new ArrayList<>();
        while (m --> 0) {
            int u = in.nextInt()-1;
            int v = in.nextInt()-1;

            rivals.add(u*n+v);
        }

        String teams = in.next();

        graph = new ArrayList<>();

        int S = 2*n;
        T = S+1;
        int N = T+1;

        for (int i=0;i<N;++i) graph.add(new HashMap<>());

        int inf = 1_000_000;

        for (int i=0;i<n;++i) {
            int i2 = i+n;

            if (teams.charAt(i) == '0') {
                graph.get(S).put(i, 2);
                graph.get(i).put(i2, inf);
                graph.get(i2).put(T, 1);
            } else {
                graph.get(S).put(i, 1);
                graph.get(i).put(i2, inf);
                graph.get(i2).put(T, 2);
            }
        }


        for (int u : rivals) {
            int v = u%n;
            u/=n;

            graph.get(u).put(n+v, inf);
            graph.get(v).put(n+u, inf);
        }

        timer = 0;
        visited = new ArrayList<>(Collections.nCopies(N, -1));

        int ans = -n;
        while (dfs(S)) {
            ++ans;
            ++timer;
        }

        System.out.println(ans);




    }
}