#include<stdio.h>
#define N 2000005

char p[N];
int main(){
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);

int i,j,n;
long nr=0;
scanf("%d",&n);
for (i = 2; i <= n; i ++) 
    if (p[i] == 0) { 
      nr++;  
       for (j = i + i; j <= n; j += i) 
         p[j] = 1;  
	   }
printf("%ld\n\n\n",nr);		
return 0;
}