from itertools import combinations
def Primes(a):
    sieve=[True]*(a+1)
    sieve[:2]=[False, False]
    sqrt=int(a**.5)+1
    for x in range(2, sqrt):
        if sieve[x]:
            sieve[2*x::x]=[False]*(a/x-1)
    return sieve

def isPrime(

def main():
    p=Primes(10**8)

main()
