#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool com[200000000];
int n, i, j, nr=0;
int main()
{
    fin>>n;
    for(i=2; i<=n/2; i++)
    {
        if(com[i] == false)
        {
            int j = i+i;
           while (j<=n)
           {
                com[j] = true;
                j +=i;
           }

        }
    }
    int nr=0;
        for(i=n; i--; i>=2)
            if(com[i] == false) nr++;
                fout<<nr-2;

}