import sys
import math

def sieve(n):
    sieve = [True] * (n + 1)
    sieve[0] = sieve[1] = False
    for i in range(2, int(math.sqrt(n)) + 1):
        if sieve[i]:
            sieve[i*i : n+1 : i] = [False] * len(sieve[i*i : n+1 : i])
    primes = [i for i, is_p in enumerate(sieve) if is_p]
    return primes

def main():
    N = int(sys.stdin.readline())
    
    if N < 2:
        print(-1)
        return
    
    max_prime_check = 2 * N
    primes_sieve = sieve(max_prime_check)
    primes_set = set(primes_sieve)
    
    primes = []
    sum_primes = []
    current_sum = 0
    for p in primes_sieve:
        if current_sum + p > N:
            break
        primes.append(p)
        current_sum += p
        sum_primes.append(current_sum)
        if current_sum == N:
            break  # Exact sum found, no need to proceed
    
    for i in range(len(sum_primes) - 1, -1, -1):
        s = sum_primes[i]
        if s > N:
            continue
        d = N - s
        if d == 0:
            print(i + 1)
            return
        p_max = primes[i]
        x = p_max + d
        if x > max_prime_check:
            continue  # Beyond sieve limit; but per sieve setup, this should be covered
        if x in primes_set:
            if i == 0:
                print(1)
                return
            else:
                if x > primes[i - 1]:
                    print(i + 1)
                    return
    
    print(-1)

if __name__ == "__main__":
    main()