#include <iostream>
#include <fstream>
#include <stdio.h>
using namespace std;
long long i,j,prime,n;
bool Prim[2000001];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    prime=1;
    for (i=2;i<=n;i+=2)
    {
        Prim[i]=true;
    }
    for (i=3;i<=n;i+=2)
    {

        if (Prim[i]==false)
        {
            cout<<i;
            prime++;
            for (j=i+i;j<=n;j=j+i)
            Prim[j]=true;
        }
    }
    g<<prime;
}