#include<stdio.h>
#define N 2000100

int v[N], n, i, j, nmax, nr; 

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