#include <iostream>

using namespace std;
//ifstream in ("ciur.in");
//ofstream out("ciur.out");

bool v[2000001];
int main()
{
    int n, i, c=0, j;
    cin>>n;
    for(i=2; i<=n; i++)
    {
        if (v[i]==0)
        {
            for(j=i*2; j<=n; j+=i)
            {
                v[j]=1;
            }c++;
        }

    }
    cout<<c;

    return 0;
}