#include <iostream>
#include <fstream>
using namespace std;
int main() {
    ifstream input("ciur.in");
    ofstream output("ciur.out");
    bool verificare=true;
    int k=1,i,prim[100],j;
    prim[1]=2;
    int n;
    input>>n;
    for(i=3;i<=n;i=i+2)
    {
        for(j=1;j<=k;j++)
            if(i % prim[j] == 0)
            {
                verificare=false;
                break;
            }
        if(verificare==true){k++;prim[k]=i;}
        verificare=true;
    }
    output<<k;
    return 0;
}