#include <iostream>
#include <cstdio>
#define Nmax 2000001
using namespace std;
bool a[Nmax];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,nr=0;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
          if(!a[i])
          {
              nr++;
              for(int j=2;j*i<=n;j++)
                 a[i*j]=1;
          }
    printf("%d",nr);
}