#include<bits/stdc++.h>
using namespace std;
const long long MaxN = 1e5 + 5;
long long n,k;
long long a[MaxN];
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    if(fopen("ANTS.inp","r"))
    {
        freopen("ANTS.inp","r",stdin);
        freopen("ANTS.out","w",stdout);
    }
    cin >> n >> k;
    for (long long i=1; i<=n; i++)
    {
        cin >> a[i];
    }
    long long ans = 0;
    for (long long i=1; i<=n; i++)
    {
        if(a[i]<0)
        {
            ans=max(ans,abs(a[i]));
        }
        else
        {
            ans=max(ans,k-a[i]);
        }
    }
    cout << ans;
}