#include <fstream>
#include <iostream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char prim[2000001];

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