#include<iostream>
#include<stdio.h>
#include<math.h>

using namespace std;

int main(){
	int n,i,j,buf,cnt;

	while(cin >> n){
		cnt = 1;

		for(i=3;i<=n;i+=2){
			buf = (int)sqrt((double)i);

			for(j=3;j<=buf;j+=2){
				if((i % j) == 0){
					cnt--;
					break;
				}
			}

			cnt++;
		}

		printf("%d\n",cnt);
	}

	return 0;
}