#include <iostream>
#include <math.h>
using namespace std;

int main(){
	int n;
	int *prime,i,j;
	int count;
	bool flag;

	while((cin >> n)!= NULL){
		count = 0;
		prime = new int[(int)sqrt(n)+1];
		for(i = 3; i <= n; i+=2){
			flag = true;
			for(j = 0; j < count; j++){
				if(i % prime[j] == 0){
					flag = false;
					break;
				}
			}
			if(flag == true){
				prime[count++] = i;
			}
		}
		if(n > 1)	count++; //2
		cout << count << endl;
		delete prime;
	}
	return 0;
}