Speed Limit

Time limit1sMemory limit128 MB

Summary

Given segments of constant speed with cumulative elapsed times, compute the total distance for each data set until n equals -1.

Level: Easy1 of 10
Topics: Implementation, Math, Simulation
Solved: No attempts yet

Problem

Bill and Ted are on a road trip, but their car's odometer is broken, so they don't know how far they have driven. Fortunately, Bill has a working stopwatch, so they can record their speed and the total time driven since the start of the trip. Their record-keeping is a little unusual, so they need help computing the total distance. Write a program to do this computation.

For example, suppose their log is:

Speed (miles per hour)	Total elapsed time (hours)
20	2
30	6
10	7

This means they drove 2 hours at 20 mph, then $6 - 2 = 4$ hours at 30 mph, then $7 - 6 = 1$ hour at 10 mph. The total distance driven is $(2)(20) + (4)(30) + (1)(10) = 40 + 120 + 10 = 170$ miles. Note that each elapsed time is measured from the beginning of the trip, not from the previous log entry.

Input

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

Output

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

Examples2

Example 1

Input

Expected output

170 miles
180 miles
90 miles

Example 2
Input
```
5
1 1
2 2
3 3
4 4
5 5
-1
```
Expected output
```
15 miles
```