#include <stdio.h>
const int MAX_V = 1000000;//1000000?????§????´???°??¨?????????
int prime [999999];//??¨?????????????????????????????????
int sum[1000000];//?´????????????????
int main(){
	
	int i, k, n;
	for(i = 2; i < MAX_V; i++){
		prime[i] = 1;
	}
	for(i = 2; i*i < MAX_V; i++){//??¨?????????????????????????????¨????????????
		if(prime[i] == 1){
			for(k = 2*i; k < MAX_V; k += i){
				prime[k] = 0;//?´???°????????°????´???°??§??????
			}
		}
	}
	for(i = 2; i < MAX_V; i++){//?´????????????????
		sum[i + 1] = sum[i] + prime[i];//
	}
	while(scanf("%d", &n) != EOF){
		printf("%d\n", sum[n + 1]);
	}
	return 0;
}