//CIURUL LUI Eratosthenes ------------------------------------------------------
#include <bits/stdc++.h>
using namespace std;
const int nmax = 2e6 + 2;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, total;
bool ciur[nmax];

int main()
{
    fin>>n;
    
    for(int i=2;i<=n;i++){
        if(ciur[i] == 0){
            total ++;
            for(int j=i;j<=n;j+=i){
                ciur[j] = 1;
            }
        }
    }
    
    fout<<total;
    
}