#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, n1, n2, u, v;
    cin >> n >> m;
    n1 = n / 2, n2 = n - n1;
    ll S;
    vector<int> edge1, edge2;
    vector<ll> edge3;
    vector<int> dp1(1 << n1, 1 << 29), dp2(1 << n2, 1 << 29);
    for(int i = 0; i < m; i++){
        cin >> u >> v;
        u--, v--;
        S = (1ll << u) | (1ll << v);
        if(max(u, v) < n1) edge1.push_back(S);
        else if(min(u, v) >= n1) edge2.push_back(S >> n1);
        else edge3.push_back(S);
    }
    S = 0;
    for(int i = 0; i < n; i++){
        cin >> v;
        S |= (ll)(v) << i;
    }
    queue<int> nxt;
    dp1[S & ((1 << n1) - 1)] = dp2[S >> n1] = 0;
    nxt.push(S & ((1 << n1) - 1));
    while(!nxt.empty()){
        v = nxt.front();
        nxt.pop();
        for(auto &&T : edge1){
            if(dp1[v] + 1 >= dp1[v ^ T])continue;
            dp1[v ^ T] = dp1[v] + 1;
            nxt.push(v ^ T);
        }
    }
    nxt.push(S >> n1);
    while(!nxt.empty()){
        v = nxt.front();
        nxt.pop();
        for(auto &&T : edge2){
            if(dp2[v] + 1 >= dp2[v ^ T])continue;
            dp2[v ^ T] = dp2[v] + 1;
            nxt.push(v ^ T);
        }
    }
    int ans = 1 << 29;
    for(int i = 0; i < (1 << edge3.size()); i++){
        S = 0;
        for(int j = 0; j < edge3.size(); j++){
            if(i >> j & 1) S ^= edge3[j];
        }
        ans = min(ans, dp1[S & ((1 << n1) - 1)] + dp2[S >> n1] + __builtin_popcount(i));
    }
    if(ans >> 29) ans = -1;
    cout << ans << '\n';
}