# A :: Speed Limit

Time Limit: 1 Second Memory Limit: 32768 KB

Bill and Ted are taking a road trip. But the odometer in their car is broken, so they don't know how many miles they have driven. Fortunately, Bill has a working stopwatch, so they can record their speed and the total time they have driven. Unfortunately, their record keeping strategy is a little odd, so they need help computing the total distance driven. You are to write a program to do this computation.

For example, if their log shows

Speed in miles per hour

Total elapsed time in hours

20

2

30

6

10

7

this means they drove 2 hours at 20 miles per hour, then 6-2=4 hours at 30 miles per hour, then 7-6=1 hour at 10 miles per hour. The distance driven is then (2)(20) + (4)(30) + (1)(10) = 40 + 120 + 10 = 170 miles. Note that the total elapsed time is always since the beginning of the trip, not since the previous entry in their log.

## Input

The input consists of one
or more data sets. Each set starts with a line containing an
integer
*n*, 1 ≤ n ≤ 10, followed
by *n* pairs of values, one pair per line. The first value in a pair,
s, is the speed in miles per hour
and the second value, t, is the
total elapsed time. Both s and t are integers, 1 ≤ s ≤ 90 and 1 ≤ t ≤ 12. The values for t are always in strictly increasing order.
A value of -1 for n signals the
end of the input.

## Output

For each input set, print the distance driven, followed by a space, followed by the word "miles".

## Sample Input

3 20 2 30 6 10 7 2 60 1 30 5 4 15 1 25 2 30 3 10 5 -1

## Sample Output

170 miles 180 miles 90 milesSubmit

Source: Mid-Central USA 2004