#include <iostream>
#include <fstream>
using namespace std;
int n,v[2000001],i,d,nr;
ofstream g("ciur.out");
int main()
{freopen ("ciur.in", "r", stdin);
scanf ("%d", &n);
for (i=1; i<=n; i++)
    v[i]=1;
for (d=2; d*d<=n; d++)
    if (v[d]==1)
        for (i=d*d; i<=n; i=i+d)
            v[i]=0;
nr=0;
for (i=2; i<=n; i++)
    if (v[i]==1)
        nr++;
g<<nr;
    return 0;
}