#include <bits/stdc++.h>

using namespace std;

ifstream fi  ("ciur.in");
ofstream fo ("ciur.out");

int n,m=1,s; 
bool v[1005];

int main()
{
	fi >> n;
	v[0] = 1;
	v[1] = 1;
	for (int i = 1 ; i <= 2000000 ; ++i)
	{
		if (v[i] == 0)
		for (int j = i+i ; j <= 2000000 ; j += i)
		v[j] = 1;
	}
	for (int i = 1 ; i <= n ; ++i)
	{
		if (v[m] == 0)
		++s;
		++m;
	}
	fo << s;
	return 0;
}