#include<stdio.h>
#include <stdlib.h>

int main(){
	int n, *a;
	int i,j;
	int result=0;
	FILE *f,*g;

	f = fopen("ciur.in","r");
	g = fopen("ciur.out","w");
	fscanf(f,"%d",&n);

	a =  (int *)calloc(n,  sizeof(int));
	a[0] = a[1] = 1;
	for(i=2;i<=n;i++)
	{
		if(a[i] == 0){
			for(j=i+i;j<=n;j+=i)
				a[j] = 1;			 
			result ++;
		}
	}

	fprintf(g,"%d",result);

return 0;
}