#include <iostream>
using namespace std;

int main(){
	int n;
	int sosu[100000];
	int snum;
	bool judge;

	sosu[0] = 2;

	while(cin >> n){
		snum = 0;
		for(int i = 3; i <= n; i++){
			judge = true;
			for(int j = 0; sosu[j]*sosu[j] < i; j++){
				if(i%sosu[j] == 0){
					judge = false;
					break;
				}
			}
			if(judge == true){
				snum ++;
				sosu[snum] = i;
			}
		}
		cout << snum + 1 << endl;
	}



	return(0);
}