#include <stdio.h>

#define MAX (100000)

int main(void)
{
	int prime[MAX + 1] = {1};
	int n;
	int ans;
	int i;
	char str[8];
	
	for (int i = 0; i <= MAX; i++){
		prime[i] = 1;
	}
	
	prime[0] = prime[1] = 0;
	i = 0;
	while (i * i <= MAX){
		while (prime[++i] != 1 && i * i <= MAX);
		//printf("%d ", i);
		for (int j = 2; j * i <= MAX; j++){
			//printf("%d\n", i * j);
			prime[i * j] = 0;
		}
	}
	
	while (fgets(str, 7, stdin)){
		sscanf(str, "%d", &n);
		
		ans = 0;
		for (int i = 2; i <= n; i++){
			if (prime[i] == 1){
				ans++;
			}
		}
	
		printf("%d\n", ans);
	}
	
	return (0);
}