Problem B
Broken Keypad
Astronauts are trained for all kinds of contingencies before launch day, and have a unique identifier number for every problem they could possibly come up with. As soon as they identify the problem, they plug the identifier into a keypad to send the information to their crew-mates and to mission control back on Earth.
A few days after the big launch, however, the “$7$” key got stuck! The protocol for this scenario is to re-assign any identifier containing a “$7$” to a different number. The astronauts are wondering how much work this will take, so as the chief coder for the mission you should write a program which counts how many identifiers in a given range of integers contain the digit “$7$” and must be re-assigned.
Input
Input consists of two space-separate integers $1 \leq a \leq b \leq 77^7 < 2 \cdot 10^{13}$.
Output
Output the number of integers in the inclusive range $[a, b]$ which contain the digit $7$.
| Sample Input 1 | Sample Output 1 |
|---|---|
1 10 |
1 |
| Sample Input 2 | Sample Output 2 |
|---|---|
8 16 |
0 |
| Sample Input 3 | Sample Output 3 |
|---|---|
700 777 |
78 |
