#include <fstream>
using namespace std;

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