#include <iostream>
#include <fstream>
#include <cmath>
#include <bits/stdc++.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
#define pb push_back
vector<int> v{2};
inline bool prime(int x)
{
    for(int i=0;v[i]<=sqrt(x);i++)
        if(x%v[i]==0)return 0;
    return 1;
}
int main()
{
    int x, i;
    f>>x;
    if(x<2)
    {
        g<<0;
        return 0;
    }
    for(i=3;i<=x;i+=2)
        if(prime(i))v.pb(i);
    g<<v.size();
    return 0;
}