package main

import (
	"fmt"
)

func main() {
	var N int
	fmt.Scan(&N)
	var ans int
	isPrime := make([]bool, N+1)
	for i := 0; i <= N; i++ {
		isPrime[i] = true
	}
	isPrime[0] = false
	for i := 2; i <= N; i++ {
		if isPrime[i] {
			ans += i
			for j := i * 2; j <= N; j += i {
				isPrime[j] = false
			}
		}
	}
	fmt.Println(ans)
}