#include <iostream>
#include <fstream>
using namespace std;
bool v[2000001];
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    int n;
    fin>>n;
    int nr=0;
    v[1]=v[0]=1;
    for (int i=2;i<=n;i++)
    {
        if (!v[i])
        {
            nr++;
            for (int j=2*i;j<=n;j+=i)
                v[j]=1;
        }
    }
    fout<<nr;
    return 0;
}