n = int(input())

l = [i+1 for i in range(n)]

ans = []
for i in l:
    if i == 1:
        pass
    elif i == 2:
        ans.append(i)
    elif i%2 == 0:
        pass
    else:
        for j in range(2, i+1):
            if i%j == 0:
                break
            if j == i-1:
                ans.append(i)

print(sum(ans))