#include <iostream>
#include <fstream>

using namespace std;
bool x[2000000];
int n,db=0;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    f >> n;
    int x[n]={0};
    x[0]=1;
    x[1]=1;
    for (int i=2;i*i<=n;i++){
        if (x[i]==0){
            for (int j=2;j<=n/i;j++){
                x[i*j]=1;
            }
        }
    }for (int j=0;j<=n-1;j++){
        if (x[j]==0)
            db++;
    }g << db;
    g.close();
    return 0;
}