The Average Miss

Northwind Grocers forecasts tomorrow's demand for every line it stocks, and by the following evening the real figure is known. The buying team wants the size of a typical miss expressed in the same unit as the goods — crates, not percentages, not anything squared — because crates are what they can hold against a pallet.

Task: Print the average size of a day's miss.

Input

The first line holds an integer n, the number of days. Each of the next n lines holds two numbers separated by a single space: the true demand first, the forecast second. Either may be whole or decimal.

Output

One line: the average miss with exactly two digits after the decimal point. A forecast three crates over and a forecast three crates under are misses of the same size, so the answer is never negative. Print 0.00 when every forecast was exact.

Example:

Input:
3
10 12
20 18
30 33

Output:
2.33