#include <iostream>
#include <fstream>

using namespace std;

    ifstream f("ciur.in");
    ofstream g("ciur.out");
    bool a[2000001];
int main()
{
    int cont=1,n,i,i2;
    f>>n;

    for(i=3;i<=n;i+=2)
    {
        if (a[i]==0)
            {cont++;
            for(i2=i;i2<=n;i2=i2+i)
                a[i2]=1;
    }}

    g<<cont;
    return 0;

}