#include<fstream>
using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

int n,o;
char v[20000005];

int main(){

    in>>n;

    for(int i=2;i<=n;i++)
        v[i]=1;


    for(int i=2;i<=n;i++)
        if(v[i]==1){
            o++;
            for(int j=i*i;j<=n;j+=i)
                v[j]=0;
        }
    out<<o;
    out.close();
    return 0;
}