#include <cstdio>
#include <vector>
#include <cmath>
#include <ctime>

using namespace std;

int main()
{
	int n;
	int len = 1;
	vector<int> prime;
	
	//unsigned long t = time(NULL);
	prime.push_back(2);
	for (int i = 3; i < 1000000; i += 2){
		int j;
		for (j = 0; j < len && prime[j] < i / 2; j++){
			if (i % prime[j] == 0){
				break;
			}
		}
		if (j >= len || prime[j] >= i / 2){
			prime.push_back(i);
			len++;
		}
	}
	//printf("%lu\n", time(NULL) - t);
	while (scanf("%d", &n) != EOF){
		int count;
		
		for (count = 0; prime[count] <= n; count++){//;
			//printf("%d\n", prime[count]);
			;
		}
		printf("%d\n", count);
	}
	
	return 0;
}