#include <iostream>
#include <queue>
#include <vector>
#include <climits>

using namespace std;

struct prots{
    int ans, data, st;
    vector <int> prev;
};

int main()
{
    prots temp1, p;
    vector <vector <int> > dp;
    vector <int> a, ans;
    queue <prots> q;
    int n, m;
    cin >> n >> m;
    a.reserve(n + 1);
    a.resize(n + 1);
    dp.reserve(n + 1);
    ans.reserve(n + 1);
    ans.resize(n + 1);
    dp.resize(n + 1);
    for (int i = 1; i <= n; i++){
        cin >> a[i];
        ans[i] = INT_MAX - 20;
        if (a[i] != 0){
            temp1.data = i;
            temp1.st = i;
            temp1.prev.push_back(i);
            temp1.ans = 0;
            q.push(temp1);
        }
    }
    int x, y;
    for (int i = 1; i <= m; i++){
        cin >> x >> y;
        dp[x].push_back(y);
        dp[y].push_back(x);
    }
    int data1;
    bool bol;
    while (!q.empty()){
        p = q.front();
        q.pop();
        for (int i = 0; i < dp[p.data].size(); i++){
            data1 = dp[p.data][i];
            bol = true;
            for (int j = 0; j < p.prev.size(); j++)
                if (data1 == p.prev[j])
                    bol = false;
            if (bol){
                if (a[data1] == 0){
                    temp1.data = data1;
                    temp1.st = p.st;
                    temp1.prev = p.prev;
                    temp1.prev.push_back(data1);
                    temp1.ans = p.ans + 1;
                    q.push(temp1);
                }
                else
                if (a[data1] != a[p.st]){
                    ans[data1] = min(ans[data1], p.ans + 1);
                    ans[p.st] = min(ans[p.st], ans[data1]);
                }
            }
        }
    }
    int min2 = ans[1];
    for (int i = 2; i <= n; i++)
        if (ans[i] < min2)
            min2 = ans[i];
    cout << min2 << "\n";
    return 0;
}

/*16 24
2 0 0 0 0 0 0 4 0 1 0 0 0 0 0 0
1 2
1 3
1 4
1 7
2 4
2 7
2 5
2 6
3 4
4 7
5 8
5 9
5 10
5 11
6 12
6 13
6 14
6 15
6 16
12 5
13 5
14 5
15 5
16 5*/