import sys
from math import gcd
from itertools import permutations
input = sys.stdin.readline

def f(x, y):
    if(gcd(x, y) == 1):
        return (x - 1) * (y - 1)
    return 0


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

ans = 10 ** 18
ops = []
if(n == 2):
    ans = f(a[0], a[1])
    ops = [(1, 2)]
elif(n == 3):
    while(len(a) > 1):
        lis1 = [-1] * 2
        lis2 = [0] * 2
        b = sorted(a)[:2]
        for i in range(2):
            for j, x in enumerate(a, 1):
                if(x != b[i] or j == lis1[0]):
                    continue
                lis1[i] = j
                lis2[i] = x
                break
        for x in lis2:
            a.remove(x)
        a.append(f(*lis2))
        ops.append(tuple(lis1))
    ans = a[0]
else:
    ans = 0
    ops = [(1, 2), (1, 2), (n - 3, n - 2)]
    for i in range(n - 3, 1, -1):
        ops.append((1, i))

print(ans)
for x, y in ops:
    if(x > y):
        x, y = y, x
    print(x, y)