#include <stdio.h>
#include<stdlib.h>
int main(){
int n,i,j,ct;
int *v;
	ct = 0;
	freopen("ciur.in","r",stdin);
	scanf("%d",&n);
	fclose(stdin);
	v = (int*) calloc(n,sizeof(int));

	for(i = 2;i<=n;i++)
		v[i] = 1;

	for(i=2;i<=n;i++)
		if (v[i] != 0){
			ct++;
			for(j = i+i;j<=n;j=j+i)
				v[j] = 0;
		}
	
	freopen("ciur.out","w",stdout);
	printf("%d",ct);
	fclose(stdout);




	return 0;
}