#include <iostream>
#include <cmath>
using namespace std;

long long sumDig(long long n)
{
	if(n<10)
	{
		int s=0;
		for(long long i=1; i<=n; i+=2)
		{
			s=s+i;
		}
		return s;
	}
	long long aux=n;
	long long nrc=0;
	while(aux)
	{
		nrc++;
		aux/=10;
	}
	nrc--;
	long long a[15];
	a[0]=0; a[1]=25;
	for (long long i=2; i<=nrc; i++)
        a[i]=(a[i-1]*10+45*ceil(pow((double)10,(double)i-1))/2);
	long long p=ceil(pow((double)10, (double)nrc));
	long long m=n/p;
	return m*a[nrc]+(m*(m-1))/2*p/2+m*(1+n%(p))/2+sumDig(n%(p));
}
long long a, b;

int main()
{
	cin>>a>>b;
	a--;
	while(a%2==0)
		a--;
	while(b%2==0)
		b--;
	cout<<sumDig(b)-sumDig(a);
}