#include <bits/stdc++.h>
using namespace std;
vector<int> edge[100005];
queue<int> q;
int a[100005], dp[100005][15];
int ind[100005];
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int n, m; cin >> n >> m;
    for (int i = 1; i <= n; i++) cin >> a[i];
    for (int i = 1; i <= m; i++){
        int u, v; cin >> u >> v;
        edge[u].emplace_back(v);
        ++ind[v];
    }
    for (int i = 1; i <= n; i++){
        if (!ind[i]) q.push(i);
        dp[i][a[i]] = 1;
    }
    while (!q.empty()){
        int u = q.front();
        q.pop();
        for (int v : edge[u]){
            if (!--ind[v]) q.push(v);
            for (int i = 1; i <= a[v]; i++)
                if (dp[v][a[v]] < dp[u][i] + 1)
                    dp[v][a[v]] = dp[u][i] + 1;
            for (int i = 1; i <= 10; i++)
                if (dp[v][i] < dp[u][i])
                    dp[v][i] = dp[u][i];
                    
        }
    }
    int maxn = -1;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= 10; j++)
            maxn = max(maxn, dp[i][j]);
    cout << maxn;
    return 0;
}