#include <iostream>
#include <fstream>
using namespace std;
int v[2000005], n, nr, i, j;
int main()
{
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin>>n;
    for (i=2; i<=n; i++)
        v[i]=1;
    for (i=2; i<=n; i++)
        if (v[i])
        {
            nr++;
            for (j=i+i;j<=n;j+=i)
                v[j]=0;
        }
    cout<<nr<<'\n';
    return 0;
}