#include<stdio.h>
int main()
{
	int n,s=0,i=1,x;
	scanf("%d",&n);
	for(;i<=n;i++)
	{	x=i;
		do{
		if(x%10==1)s++;
		x=x/10;
		}while(x!=0);
	}
	printf("%d",s);
 	return 0;
}

/**************************************************************
	Problem: 1448
	User: admin
	Language: C
	Result: Accepted
	Time:20 ms
	Memory:1144 kb
****************************************************************/