#include <iostream>
#include <bitset>
#define MAX 2000002

using namespace std;

char prime[MAX];
int n, cnt;

int main(){
	int i, j;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	for(i = 2; i <= n; i++){
		if(!prime[i]){
			cnt++;
			for(j = i * i; j <= n; j+=i){
				prime[j] = 1;
			}
		}
	}
	printf("%d\n", cnt);
	return 0;
}