#include <iostream>
#include <fstream>

using namespace std;

int main ()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,i,j,db=0;
    f>>n;
    bool X[n+1];
    X[0]=X[1]=false;

    fill(X,X+n+1,true);

    for (i=2;i<n+1;i++)
    {
        if (X[i])
        {
            db++;
            for (j=i;j<n+1;j+=i)
            {
                X[j]=false;
            }
        }
    }
    g<<db;
}