#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <map>
#include <set>

using namespace std;

#define mp make_pair
#define pb push_back
#define sz(c) (int)((c).size())
#define f first
#define s second

#define fin  "ciur.in"
#define fout "ciur.out"

#define NMAX 2000001

int N;
char v[NMAX];

int main()
{
	int i, j, count = 1, tmp;
	
	ifstream f(fin);
	ofstream f2(fout);

	f >> N;
	memset(v,0,sizeof(v));
	for ( i = 3; i <= N; i += 2 )
		if ( !v[i] )
		{
			++count;
			for ( j = (tmp = (i << 1)) + i; j <= N; j += tmp )
				v[ j ] = 1;
		}

	f2 << count << endl;

	return 0;
}