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
## 解答
```cpp
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
int main()
{
int num, i;
cin >> num;
vector<int> arr(num, 0);
for (i = 0; i < num; i++)
cin >> arr[i];
sort(arr.begin(), arr.end(), greater<int>());
for (i = 0; i < num; i++) {
if (i + 1 >= arr[i]) break;
}
cout << i;
return 0;
}
```

PAT A1117 Eddington Number (25point(s))