#include<iostream>
#include<fstream>
#include<cstring>
#include<bits/stdc++.h>
#include<iomanip>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
	
int main()	
{
    ios::sync_with_stdio(0);
    fin.tie(0); 
    long long n;
    cin>>n;
    vector<int> ciur(n,0);
    ciur[0] = ciur[1] = 1;
    for(int i=2;i*i<=n;i++)
    {
        if(ciur[i] == 0)
        {
            for(int j=i+i;j<=n;j+=i)
                ciur[j] = 1;
        }
    }
    int counter = 0;
    for(int i=2;i<=n;i++)
    {
        if(ciur[i] == 0)
            counter++;
    }
    cout<<counter;
    fout.tie(0);
    fin.close();
    fout.close();
    return 0;
}