//0009 Prime Number
//100¢Ì³Ì®nªüÍ³ê½Æ«AnÈºÌfª¢­ç é©oÍ·évOðì¬¹æ
//s²ÆÉêÂÌ®nªüÁÄ¢é@EOFªüÍÌIíèÅ é

#include<iostream>
#include<bitset>
using namespace std;

int main(void)
{
	const int N = 1000000;	//100ÂmÛ
	bitset<N> isPrime;
	int n;
	int i, j;

	while( cin >> n)
	{
		//â¿ðg¢Ü·
		isPrime.set();
		isPrime[0] = isPrime[1] = false;
		for(i = 2; i <= n; i++)
		{
			if(isPrime[i])
			{
				for(j = 2*i; j <= n; j+=i)
				{
					isPrime[j] = false;
				}
			}
		}

		int count = 0;
		for(i = 0; i <= n; i++)
			if(isPrime[i])
				count++;

		cout << count << endl;
	}
	return 0;
}