mx = 10**18
fib = [0 for _ in range(10**5)]
fib[0] = 1
fib[1] = 1
rfib = {}
rfib[1] = 1
for i in range(2, len(fib)):
    fib[i] = fib[i-1] + fib[i-2]
    if fib[i] > mx:
        break
    rfib[fib[i]] = i

n, m = map(int, input().split())
heights = list(map(int, input().split()))
mansions = list(range(n))
pred = {a:[] for a in mansions}
for i in range(m):
    a, b  = map(int, input().split())
    a -= 1
    b -= 1
    ha = heights[a]
    hb = heights[b]
    if ha in rfib and hb in rfib:
        if rfib[ha] == rfib[hb] + 1:
            pred[a].append(b)
        elif rfib[hb] == rfib[ha] + 1:
            pred[b].append(a)
        if ha == hb and ha == 1:
            pred[a].append(b)
            pred[b].append(a)
mansions = sorted(mansions, key=heights.__getitem__)
visited = [1]*n
for i in range(n):
    M = mansions[i]
    if heights[M] == 1 and len(pred[M]) > 0:
        visited[M] = 2
    elif heights[M] in rfib:
        visited[M] = max([visited[j] for j in pred[M]]+[0])+1


has_any_fib = False

for i in range(n):
    if heights[i] in rfib:
        has_any_fib = True
        break

if not has_any_fib:
    print(0)
else:
print(max(visited))