#include <bits/stdc++.h>

using namespace std;

namespace FastRead{
	char buf[1000005], *s = buf, *t = buf, ch, f;
	#define gc() s == t && (t = (s = buf) + fread(buf, 1, 1000000, stdin), s == t) ? EOF : *s ++ 
	template <typename T>
	inline void Read(T &x)
	{
		x = f = 0, ch = gc();
		while(ch < '0' || ch > '9') f = ch == '-', ch = gc();
		while('0' <= ch && ch <= '9') x = x * 10 + ch - 48, ch = gc();
		f && (x = -x);
	}
};
using FastRead::Read;

const int N = 6e5 + 5, INF = 0x3f3f3f3f;

int n, m, c[N];
int la[N], ne[N], en[N], idx;
int dis[N], deg[N], q[N], hh, tt;

inline void Add(int a, int b)
{
    // printf("#%d %d\n", a, b);
    ne[ ++ idx] = la[a];
    la[a] = idx;
    en[idx] = b;
    deg[b] ++ ;
}
inline void Topo()
{
    memset(dis, 0x3f, sizeof dis);
    hh = 0, tt = -1;
    for(int i = 1; i <= n * 2; i ++ )
        if(!deg[i])
        {
            dis[i] = 1;
            q[ ++ tt] = i;
        }
    while(hh <= tt)
    {
        int u = q[hh ++ ];
        for(int i = la[u]; i; i = ne[i])
        {
            int v = en[i];
            deg[v] -- ;
            if(!deg[v])
            {
                dis[v] = dis[u] + 1;
                q[ ++ tt] = v;
            }
        }
    }
}

int main()
{
    Read(n), Read(m);
    for(int i = 1; i <= n; i ++ ) Read(c[i]);
    for(int i = 1; i <= m; i ++ )
    {
        int a, b;
        Read(a), Read(b);
        if(c[a] == c[b]) Add(a + n, b), Add(b + n, a);
        else Add(a, b + n), Add(b, a + n);
    }
    Topo();
    int mx0[2] = {0, 0}, mx1[2] = {0, 0};
    for(int i = 1; i <= n; i ++ )
    {
        mx0[c[i]] = max(mx0[c[i]], dis[i]);
        mx1[c[i]] = max(mx1[c[i]], dis[i + n]);
    }
    int ans = min(min(mx0[0], mx0[1]), min(mx1[0], mx1[1])) + 1;
    if(ans >= INF) puts("infinity");
    else printf("%d\n", ans);
    return 0;
}