#include <cstdio>
#include <vector>

using namespace std;

#define N 2000005
vector<bool> 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(){
    //timer t;
    int i;
    v.resize(N);
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    printf("%d\n",ciur());
    return 0;
}