#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool b[50000001];

int main(){
	int n, k = 1;
	fin>>n;
	for(int i = 1;((i*i)<<1) + (i<<1) <= n; ++i)
	if(!b[i])
		for(int j = ((i*i)<<1) + (i<<1);(j<<1) + 1 <= n; j += (i<<1) + 1)
			b[j] = 1;
	for(int i = 1;(i<<1) + 1<= n; ++i)
		if(!b[i])
			++k;
	fout<<k;
	return 0;
}