#include <iostream>
#include <stdio.h>
using namespace std;

bool prime[2000001];
int cnt;

int main()
{
    int n ;
    freopen("ciur.in","r",stdin);
    scanf("%d",&n);

    for(int i = 2 ; i <= n ; ++ i )prime[i]=true;

    for(int i = 2;  i <=n ; ++ i )
        if(prime[i])
        {++cnt;
         for( int j = i + i ; j <= n ; j += i )
            prime[j]=false;
        }
freopen("ciur.out","w",stdout);
printf("%d",cnt);



    return 0;
}