#include <bits/stdc++.h>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int d,i,nr,n;
bool a[2000010];

int main()
{
    for(d=2;d*d<=2000000;d++)
    {
        if(a[d]==0)
        {
            for(i=d*d;i<=2000000;i+=d)
                a[i]=1;
        }
    }

    f>>n;
    for(i=2;i<=n;i++)nr=nr+(1-a[i]);
    g<<nr;
    return 0;
}