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## Problem Description

After doing setsquare, Guan has acquired a new brilliant plan :D

On a street with **N** grids, where each grid has a height limit **Hi**, Guan wishes to erect a half-pyramid hotel

The half-pyramid hotel must face right (i.e. from left to right the height of the hotel will be strictly decreasing)

The heights of the buildings constituting the hotel must be a sequence of consecutive numbers, with the smallest consecutive number being 1

I.e. from left to right, 3,2,1 or 4,3,2,1 or 6,5,4,3,2,1

Guan wants to find out the maximum height of the largest possible pyramid hotel he can erect. Help him

## Input

The first line contains the number of city grids, **N**

The next **N** lines contain the height limit of each grid, **Hi**, from left to right

## Constraints

1<=**Hi**<=1,000,000

1<=**N**<=1,000,000

## Output

A single number, the maximum height of the largest possible pyramid hotel Guan can erect

## Subtasks

Subtask 1 (3%) **Hi**=**N**-i (i starts from 1 and ends with N)

Subtask 2 (23%) **N**<=**1,000**

Subtask 3 (74%) **N**<=**1,000,000**

## Warning

Please use scanf/printf or put the line ios_base::sync_with_stdio(false) if using cin/cout (And avoid using scanf/printf), or you will TLE

## Sample Testcase 1

Input

6 6 5 4 3 2 1Output

6

## Explanation

Guan builds a hotel from the leftmost grid of heights 6,5,4,3,2,1

## Sample Testcase 2

Input

6 1 2 3 4 5 6Output

3

## Explanation

Guan builds a hotel of 3,2,1 on the tiles with a height limit of 3,4,5 respectively

### Tags

### Subtasks and Limits

Subtask | Score | #TC | Time | Memory | Scoring |
---|---|---|---|---|---|

1 | 3 | 10 | 0.5s | 64MB | Minimum |

2 | 23 | 11 | 0.5s | 64MB | Minimum |

3 | 74 | 11 | 0.5s | 64MB | Minimum |

4 | 0 | 2 | 0.5s | 64MB | Minimum |

### Judge Compile Command

g++-7 ans.cpp -o pyramidhotel -Wall -static -O2 -lm -m64 -s -w -std=gnu++17 -fmax-errors=512