#include <fstream>
# define N 2000001
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
int v[N],n,i,j,nr;
int main()
{
    f>>n;
    i=2;
    while(i*i<=n)
    {
        if(v[i]==0)
        {
            v[i]++;
            nr++;
            for(j=i*i;j<=n;j=j+i)
                v[j]++;
        }
        i++;
    }
    for(j=i+1;j<=n;j++)
        if(v[j]==0)
            nr++;
    g<<nr;
    return 0;
}