# include <fstream>
# include <math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
long n,i,j;
bool p[2000001];
int k;
int main()
{
    f>>n;
    k=0;
    for(i=2;i<=sqrt(n);++i)
    {
        if(p[i]==0)
        {
            for(j=i+i;j<=n;j=j+i)
            {
                p[j]=1;
            }
        }
    }
    for(i=2;i<=n;i++)
    {
        if(p[i]==0) k++;
    }
    g<<k<<'\n';
    return 0;
}