#include <iostream>
#include <fstream>

using namespace std;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    bool a[2000001];
int main()
{
    int n,i,i2,cont=1;
    f>>n;
    for(i=3;i<=n;i=i+2)
    {
        if (a[i]==0)
        {
            cont++;
            for(i2=i;i2<=n;i2=i2+i)
                a[i2]=1;
        }
    }
    g<<cont;


    return 0;
}