from math import *
from copy import *

inf = 10 ** 18
def f(x, y):
    if gcd(x, y) != 1:
        return 0
    v = (x - 1) * (y - 1)
    if v >= inf:
        return -1
    return v    

N = int(input())
A = list(map(int, input().split()))
if N == 2:
    print(f(A[0], A[1]))
    print(1, 2)
elif N == 3:
    v = inf
    T = [(1, 2), (1, 2)], [(1, 3), (1, 2)]
    ans = []
    for tt in T:
        D = deepcopy(A)
        for t in tt:
            temp = f(D[t[0] - 1], D[t[1] - 1])
            D.pop(t[1] - 1)
            D.pop(t[0] - 1)
            if temp == -1:
                break
            D.append(temp)
        else:
            if D[0] < v:
                ans = tt
                v = D[0]
    print(v)
    for a, b in ans:
        print(a, b)
else:
    def f1(A , ans=[]):
        ind1, ind2 = -1, -1
        N = len(A)
        for i in range(N):
            if ind1 == -1:
                if A[i]%2 == 0:
                    ind1 = i + 1
            else:
                if A[i]%2 == 0:
                    ind2 = i + 1
        if ind2 != -1:
            print(0)
            for a, b in ans:
                print(a, b)
            print(ind1, ind2)
            for i in range(N - 1, 1, -1):
                print(1, i)
            exit()
            
    def f2(A):
        ind1, ind2 = -1, -1
        N = len(A)
        for i in range(N):
            if ind1 == -1:
                if A[i]%2 == 1:
                    ind1 = i + 1
            else:
                if A[i]%2 == 1:
                    ind2 = i + 1
        v = (A.pop(ind2 - 1) - 1) * (A.pop(ind1 - 1) - 1)
        A.append(v)
        return (ind1, ind2), A
            
    t, A = f2(A)
    ans = [t]
    f1(A, ans)
    t, A = f2(A)
    ans.append(t)
    f1(A, ans)