#include <fstream>
using namespace std;

int main()
{   ifstream f("ciur.in");
    ofstream g("ciur.out");
    
    int n,cnt = 1,prim[2000002],i,j;
    f >> n;
    for(i = 2;i <= n;i++)prim[i] = 1;
    for(i = 3;i <= n;i=i+2){
    if(prim[i] == 1){cnt++;
    for(j = 2;j*i <= n;j++)prim[i*j] = 0;
    }
    }
    g << cnt;
    f.close();
    g.close();
    
    
    
    
  return 0;
}