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

int main()
{
    int c[100], n, i, j,nr=0;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;

for(i=1;i<=n; i++) c[i] =1;

for (i=2;i<=n;i++)

    if(c[i] == 1)

         for(j=2;j*i <= n;j ++)  c[i*j] = 0;

for(i=2;i<=n; i++)

    if(c[i] ==1) nr++;
    g<<nr;


    return 0;
}