#include <fstream>
using namespace std;
int n, contuar = 0;
char v[2000005];
ifstream ciurin("ciur.in");
ofstream ciurout("ciur.out");
int main()
{
    ciurin >> n;
    for(int i=2;i<= n;i++)
    {if(v[i]==0){contuar++;for(int d=i*i;d<=n;d=d+i){v[d] = 1;}}}
    ciurout << contuar;
    ciurin.close();
    ciurout.close();
    return 0;
}