#include <iostream>
#include <math.h>
#include <fstream>
using namespace std;

int main()
{
char nr[2000002];
int n,i,j,s=1;
//cin>>n;
ofstream scr("ciur.out");
ifstream c("ciur.in");
c>>n;
    for (i=3;i<=n/2;i=i+2){
    if (!nr[i]){
        for (j=2*i;j<=n;j=j+i){
            nr[j]=1;
        }
    }
    }
for (i=3;i<=n;i=i+2)
    if(nr[i]==0)
    s=s+1;
scr<<s;

}