#include <iostream>
#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char prim[2000005];
int n,nr=0;

 int main()
{ int i,j;

  f>>n;
for (i=2;i<=n;i++)
{ prim[i]=1;
for(i=2;i<=n;i++)
{ if (prim[i])
{ nr++;
    for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }


}
g<<nr;
    return 0;
}