#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,cont;
bool p[2000005];
int main()
{
    fin>>n;
    for(i=2;i<=n;i++)
    {
        if(p[i]==0)
        {
            cont++;
        for(j=1;j<=n/i;j++)
        {
            p[i*j]=1;
        }
        }
    }
    fout<<cont;
    return 0;
}