#include<stdio.h>
#include <bitset>
#define Nmax 2000005

using namespace std;

bitset<Nmax> V;
int N, x;

int ciur(){
     int i, j, nr = 1;
     x = 1;
     for (i = 3; i <= N ; i += 2)
        if (V[i] == false){
           ++x;
           ++nr;
           if (i <= 32000)
              for (j = i * i; j <= N; j += i)
                  V[j] = true;
        }
     return nr;
}
int main(){
    int i;
    
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &N);
    
    printf("%d\n",ciur());

}