#include <bits/stdc++.h>


using namespace std;



int main(){

 ifstream cin("ciur.in");
 ofstream cout("ciur.out");
int N;
unsigned char prim[2000005];
cin >> N;
int count = 0;
//if(N % 2 == 0) count++;

for(int i = 3; i <= N; i+= 2)
{
  if(!prim[i])
  {
    count++;
    for(int j = i + i; j < N; j+=i ) prim[j] == 1;
     
  }
}

cout << count;

}