Problem:
Score : 300 points

Problem Statement

There is a circular pond with a perimeter of K meters, and N houses around them.

The i-th house is built at a distance of A_i meters from the northmost point of the pond, measured clockwise around the pond.

When traveling between these houses, you can only go around the pond.

Find the minimum distance that needs to be traveled when you start at one of the houses and visit all the N houses.

Constraints

2 \leq K \leq 10^6

2 \leq N \leq 2 \times 10^5

0 \leq A_1 < ... < A_N < K

All values in input are integers.

Input

Input is given from Standard Input in the following format:

K N
A_1 A_2 ... A_N

Output

Print the minimum distance that needs to be traveled when you start at one of the houses and visit all the N houses.

Sample Input 1

20 3
5 10 15

Sample Output 1

10

If you start at the 1-st house and go to the 2-nd and 3-rd houses in this order, the total distance traveled will be 10.

Sample Input 2

20 3
0 5 15

Sample Output 2

10

If you start at the 2-nd house and go to the 1-st and 3-rd houses in this order, the total distance traveled will be 10.

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

#define int         long long
#define mp          make_pair
#define pb          push_back
#define vi          vector<int>
#define vii         vector<pair<int,int>>
#define mi          map<int,int>
#define mii         map<pair<int,int>,int>
#define all(a)      (a).begin(),(a).end()
#define f           first
#define s          second
#define sz(x)       (int)x.size()
#define endl        '\n'
#define hell        1000000007
#define hellhsh     444440583533
#define rep(i,a,b)  for(int i=a;i<b;i++)
#define rep0(a,n)  for(int i=0;i<n;i++)cin>>a[i];
#define si(x)       cin>>x;
#define sii(x,y)    cin>>x>>y;
#define ahell   998244353
#define p(x)   printf("%I64d",x)
#define aut(x,u) for(auto x:u)
#define pri     queue<pii>
#define forn(k) for(int i=0;i<k;i++)
#define N 200007
#define fl 1.0000000000
#define ms(a,n) memset(a,n,sizeof(a))
#define INF 10000000000007
using namespace std;
int x,y,m,k;
int n;
vii list[1006];
void solve()
{
int q=0,i,j;
int x,y=0,ct=0;
cin>>k>>n;
int a[n];
rep0(a,n);
y=0;
y=max(a[n-1]-a[0],y);
for(i=1;i<n;i++)
  y=max(y,a[i]-a[i-1]);
cout<<k-y;

}
main()
{
ios_base::sync_with_stdio(false); 
    cin.tie(NULL); 
    int i,j,k,test=1;
    
  //cin>>test;
  while(test--)
  {
      solve();
      //cout<<"\n";
 }

}