#include <cstdio>
#include <vector>
#include <ctime>
 
using namespace std;
 
int main()
{
    int n;
    vector<int> prime;
     
    //unsigned long t = time(NULL);
    prime.push_back(2);
	prime.push_back(3);
    while (scanf("%d", &n) != EOF){
		if (prime[prime.size() - 1] <= n){
			for (int i = prime[prime.size() - 1] + 2; i <= n; i += 2){
				bool p = true;
				for (int j = 0; prime[j] <= i / 2; j++){
					if (i % prime[j] == 0){
						p = false;
						break;
					}
				}
				if (p){
					prime.push_back(i);
				}
			}
		}
		
		int count;
		for (count = 0; count < prime.size() && prime[count] <= n; count++){
			;
		}
		printf("%d\n", count);
    }
     
    return 0;
}