#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include <map>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <stack>
#include <algorithm>
#include <array>
#include <unordered_set>
#include <unordered_map>
#include <string>
using namespace std;

bool rcmp(int a, int b) { return a>b; }
typedef long long LL;



int as[64], bs[64], cs[64];
int main() {
    int n, i, a, b, d, m;
    LL v, one=1, nv;
    scanf("%d %d", &n, &m);
    for (i=0; i<m; i++) {
        scanf("%d %d", &as[i], &bs[i]);
        as[i]--; bs[i]--;
    }
    v=0;
    a=0;
    for (i=0; i<n; i++) {
        scanf("%d", &cs[i]);
        a+=cs[i];
    }
    if (a&1) {
        printf("-1\n"); return 0;
    }
    for (i=n-1; i>=0; i--) {
        v=v*2+cs[i];
    }
    queue<LL> q;
    map<LL, int> dp;
    dp[v]=0;
    q.push(v);
    while(!q.empty()) {
        if (dp.count(0)) break;
        v = q.front();
        d = dp[v]+1;
        q.pop();
        for (i=0; i<m; i++) {
            a=as[i]; b=bs[i];
            nv = v^(one<<a)^(one<<b);
            if (dp.count(nv)) continue;
            dp[nv]=d;
            q.push(nv);
        }
    }
    if (dp.count(0)) printf("%d\n", dp[0]);
    else printf("-1\n");
            
    return 0;
}