def make_divisors(n):
    from collections import deque
    divisors = deque([])
    for i in range(1, int(n**0.5)+1):
        if n % i == 0:
            divisors.append(i)
            if i != n // i:
                divisors.append(n//i)
    lst_divisors = list(divisors)
    lst_divisors.sort()
    return lst_divisors

X = int(input())

n_div = [0]*(X+1)

d = {}
for a in range(1, X//2+1):
    b = X-a
    n_div[a] = len(make_divisors(a))
    n_div[b] = len(make_divisors(b))
    f = abs((a-n_div[a])-(b-n_div[b]))
    if f not in d:
        d[f] = [[a, b]]
    else:
        d[f].append([a, b])

print(min(d.keys()))

ans = sorted(d[min(d.keys())])
for v in ans:
    a, b = v
    print(a, b)
    
for v in ans[::-1]:
    a, b = v
    if a != b:
        print(b, a)