#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <iterator>
#include <random>
#include <assert.h>
using namespace std;

const string file = "ciur";

const string infile = file + ".in";
const string outfile = file + ".out";

const int INF = 0x3f3f3f3f; 

//#define ONLINE_JUDGE


int ciur(int N)
{
    int result = 1;
    vector<bool> A(N + 1);
    int sqr = sqrt(N) + 1;
    for(int i = 4; i <= N; i += 2)
    {
        A[i] = true;
    }
    for(int i = 3; i <= N; i += 2)
    {
        if(A[i] == false)
        {
            result++;
            if(i > sqr)
                continue;
            for(int j = i * i; j <= N; j += 2 * i)
            {
                A[j] = true;
            }
        }
    }


    return result;
}

int main()
{
#ifdef ONLINE_JUDGE
	ostream &fout = cout;
	istream &fin = cin;
#else
	fstream fin(infile.c_str(), ios::in);
	fstream fout(outfile.c_str(), ios::out);
#endif	

    int N;
    fin >> N;
    
    fout << ciur(N) << "\n";

#ifdef ONLINE_JUDGE
#else
    fout.close();
	fin.close();
#endif
}