#include<stdio.h>
int main()
{
	int i,n,b,t,c=0;
	scanf("%dd",&n);
	for(i=1;i<=n;i++)
	{
		t=i;
		while(t>0)
		{
			b=t%10;
			if(b==0)
			{
				c++;
				break;
			}
			t=t/10;
		}
	}
	printf("%d",c);
	return 0;
}
/**************************************************************
	Problem: 1750
	User: admin
	Language: C
	Result: Accepted
	Time:15 ms
	Memory:1144 kb
****************************************************************/