#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;

int n,a[2000005],p;
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in >> n;
    p=0;
    int s = sqrt(n);
    for(int i=1;i<=n;i++) a[i]=0;
    for(int i=2;i<=s;i++){
        if(a[i]==0){
            for(int j=2;j*i<=n;j++){
                a[i*j]=1;
            }
        }
    }
    for(int i=2;i<=n;i++){
        if(a[i]==0) p++;
    }
    out << p;
}