s = 2; N = 2000001; primeSum = [0]*(N+1)
for i in range(3, N, 2):
    if primeSum[i]==0:
        s+= i
        primeSum[i::i] = [-1]*(N//i)
    primeSum[i:i+2] = [s, s]
L = int(input("Sum of primes below "))-1
print ("is", primeSum[L])