bfs

#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#include <string>
#include <stack>
#include <set>
#include <map>
#define pii pair <int, int>
#define pb(x) push_back(x)
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
void cv(vector <int> &v) {
    for (auto x : v) cout << x << ' ';
    cout << "\n";
}

void cvl(vector <ll> &v) {
    for (auto x : v) cout << x << ' ';
    cout << "\n";
}


void cvv(vector <vector <int> > &v) {
    for (auto x : v) cv(x);
    cout << "\n";
}

void cvb(vector <bool> v) {
    for (bool x : v) cout << x << ' ';
    cout << "\n";
}

void cvs(vector <string>  v) {
    for (auto a : v) {
        cout << a << "\n";
    }
}

void cvp(vector <pii> a) {
    for (auto p : a) {
        cout << p.first << ' ' << p.second << "\n";
    }
    cout << "\n";
}

int n, m;

vector <pii> G;
vector <int> d;
int inf = 2e9;

void bfs() {
    d[0] = 0;
    deque <int> Q;
    Q.push_back(0);
    while (!Q.empty()) {
        int v = Q.front();
        Q.pop_front();
        for (pii e: G[v]) {
            int u = e.first, w = e.second;
            if (d[u] != inf) {
                continue;
            }
            if (d[u] > d[v] + w) {
                d[u] = d[v] + w;
                if (w == 0) {
                    Q.push_front(u);
                } else {
                    Q.push_back(u);
                }
            }
        }
    }
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n >> m;
    vector <int> kng(n,-1);
    for (int &i: kng) cin >> i;
    G.resize(n);
    d.assign(n, inf);
    for (int i = 0; i < n; ++i) {
        int a, b; cin >> a >> b;
        a--;
        b--;
        int w = 1;
        if (kng[a] == kng[b]) {
            w = 0;
        }
        pii ab = {b, w};
        pii ba = {a, w};
        G[a].pb(ab);
        G[b].pb(ba);
    }

    bfs();
    if (d[n - 1] == inf) {
        cout << "impossible";
        exit(0);
    }

}