769B - News About Credit - CodeForces Solution

n = int(input())
l = list(map(int, input().split()))

a = [[l[i], i + 1] for i in range(n)]
a = [a[0]] + sorted(a[1:], key = lambda a: a[0], reverse = True)

f, t = 0, 1
p = []

while t < n:
	if a[f][0] == 0:
		t = 0
		break
	
	p.append([a[f][1], a[t][1]])	
	a[f][0] -= 1
	t += 1
	
	if a[f][0] == 0:
		f += 1
		
print(t - 1)

if t > 0:
	for i in p:
		print(i[0], i[1])