#include<stdio.h>
long n,k,i,j;   
int a[2000001];
int main(){   
  
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);

scanf("%ld",&n);

for(i=2;i<=n;i++)
		if(a[i]==0)
		{
		for(j=2*i;j<=n;j=j+i)if(j<n)a[j]=1;
		k++;
		}

printf("%ld",k-1);
return 0;
}