#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int  n;
bool v[2000000];
int main()
{
	int nr=1,i,j,ok;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	for (i = 3; i <= n; i += 2){
		if (v[i] == false){
			nr++;
			for (j = 3 * i; j <= n; j += 2 * i)
				v[j] = true;
		}
	}
     
	printf("%d", nr);
	return 0;
}