#include<iostream>
using namespace std;
int f(int m)
{
	if(m==1||m==2)
	return 1;
	else
	return f(m-1)+f(m-2);
}
int main()
{
int c,d,sum=0,i;
cin>>c>>d;
for(i=c;i<=d;i++)
{
	sum+=f(i);
}
cout<<sum;
}