#include <iostream>
#include <fstream>

using namespace std;

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

const int MAX=2e6+1;
bool v[MAX];

int main()
{
    int n;
    in>>n;
    int s=0;
    for(int i=2;i<=n;i++){
        if(v[i]==0){
            for(int j=i+i;j<=n;j+=i){
                v[j]=1;
            }
            s=s+1;
       }
    }
    out<<s;
    return 0;
}