#include<cstdio>
#include<vector>
using namespace std;
int main(void){
	int n;
	vector<int> a;
	int c;
	a.push_back(2);
	a.push_back(3);
	for (int i = 2; i < 510000; i++){
		for (int j = 1; j < a.size(); j++){
			if (a[j] * a[j]>2*i+1){
				a.push_back(2*i+1);
				break;
			}
			if ((2*i+1)%a[j] == 0)break;
		}
	}

	while (scanf("%d", &n) != EOF){
		c = 0;
		for (int i = 0; a[i] <= n; i++)c++;
		printf("%d\n", c);
	}
	return 0;
}