#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool p[2000005];
int main()
{
    int n,nrp=0;
    long long i,j;
    in>>n;
    for(i=2;i<=n;i++){
        if(p[i]==0){
            nrp++;
            for(j=i*i;j<=n;j=j+i){
                p[j]=1;
            }
        }
    }
    out <<nrp;
    return 0;
}