#include <fstream>
#include <vector>
#include <iostream>

#define tip long

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    tip i, k, n;
    fin>>n;
    vector<int>v(n+1, 0);
    tip sol=0;

    for(i=2; i<=n; ++i)
    {
        if(v[i]!=1)
        {
            sol++;
            k=i;
            while(k<=n)
            {
                v[k]=1;
                k=k+i;
            }
        }
    }
    fout<<sol;
}