1117 Eddington Number （25 分）

British astronomer Eddington liked to ride a bike. It is said that in order to show off his skill, he has even defined an "Eddington number", E -- that is, the maximum integer E such that it is for E days that one rides more than E miles. Eddington's own E was 87.

Now given everyday's distances that one rides for N days, you are supposed to find the corresponding E (≤N).

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤10​5​​), the days of continuous riding. Then N non-negative integers are given in the next line, being the riding distances of everyday.

Output Specification:

For each case, print in a line the Eddington number for these N days.

Sample Input:

10
6 7 6 9 3 10 8 2 7 8

Sample Output:

6

 題目大意：E是有E天騎行超過E的最大整數。

 對於本題輸出6，有7 9 10 8 7 8這6天是超過6的，等於6的不算，所以得出了6.

//發現自己並不會寫，不會寫啊！！好難啊！這個邏輯！！！

柳神的解答:

//雖然題幹挺短，但是邏輯挺難的，