n = io.read("*n")
sum = 0
if 1 < n then sum = 2 end
p = {}
for i = 3, n, 2 do
    found = false
    for k, v in pairs(p) do
        if(i % v == 0) then found = true; break end
    end
    if not found then
        sum = sum + i
        table.insert(p, i)
    end
end
print(sum)