n=int(input())
prim = [1]*(n+1)
cnt = 0

for i in range(3,n+1,2):
    for j in range(i*2,n+1,i):
        prim[j]=0

for i in range(3,n+1,2):
    if prim[i]==1:
        cnt+=i

if n>=2:
    cnt+=2

print(cnt)