#include<iostream>
using namespace std;

int main(){
	int n;
	while(cin >> n){
		bool* p = new bool[n+1];
		int cou = 0;
		for(int i = 0; i < n+1; ++i){
			p[i] = true;
		}
		p[0] = false; p[1] =false;
		for(int i = 2; i*i <= n; ++i){
			for(int j = 2;i*j <= n ; ++j) {
				p[i*j] = false;
			}
		}

		for(int i = 0; i < n+1; ++i ){
			if(p[i] == true) ++cou;
		}
		cout << cou << endl;
	}
    return 0;
}