#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>
using namespace std;

const string file = "ciur";

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

const int INF = 0x3f3f3f3f;
int N;
int Sol;

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

int main()
{
	fstream fin(infile.c_str(), ios::in);
	fin >> N;
	fin.close();
	ciur();
	fstream fout(outfile.c_str(), ios::out);
	fout << Sol << "\n";
	fout.close();
}