PROGRAMMING:Add up a-aa + AAA AAAA +

Calculate the value of a-aa + AAA AAAA +... And the last item is n a. the values of a and N are input by keyboard. A and N are positive integers, and the result of accumulation is defined as double precision real type.
###Input format:
The values of a and N are entered on one line, separated by spaces.
###Output format:
When outputting, the result only retains the integer part and is output in the form of output sample.
###Input example:
```in
2 5
```
###Output example:
```out
sum=20202
```
###Input example:
```in
2 12
```
###Output example:
```out
sum=-202020202020
```







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