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