#include<iostream>
#include<cstdio>
using namespace std;

int main() {
	int n;
	while(cin >> n && n != EOF) {
		bool* prime = new bool[n+1];
		int count = 0;
		for(int i = 0; i <= n; ++i) {
			prime[i] = true;
		}
		prime[0] = prime[1] = false;
		
		for(int i = 0; i <= n; ++i) {
			if(prime[i]) {
			//	cout << i << '\t';
				for(int j = 2 * i; j <= n; j += i) {
					prime[j] = false;
				}
			}
		}
		
		for(int i = 0; i <= n; ++i) {
			if(prime[i]) {
				count++;
			}
		}
		
		cout << count << endl;
		delete[] prime;
	}
}