#include <bits/stdc++.h>
using namespace std;

int main(void) {
	vector<int> v;
	v.push_back(2);
	v.push_back(3);
	int i, j;
	bool flag;
	for (i = 5; i < 999999; i++) {
		flag = true;
		for (j = 2; j <= sqrt(i); j++) {
			if (i % j == 0) {
				flag = false;
				break;
			}
		}
		if (flag) {
			v.push_back(i);
		}
	}
	int n;
	while (cin >> n) {
		i = distance(v.begin(), lower_bound(v.begin(), v.end(), n));
		if (v[i] == n)
			cout << i + 1 << endl;
		else 
			cout << i << endl;
	}

}
