def mark(s, x):
    for i in xrange(x + x, len(s), x):
        s[i] = False

def sieve(n):
    s = [True] * n
    for x in xrange(2, int(n**0.5) + 1):
        if s[x]: mark(s, x)
    return [i for i in xrange(0,n) if s[i] and i > 1]


print sum(sieve(int(input())+1))