#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,c,l,r,mid,maxi,a[1000005];
bool check(int mid){
    ll x=0,flag=a[1];
    for(int i=1;i<=n;i++){
        if(x<mid){
			x=a[i]-flag;
		}
    }
    return x<mid;
}
int main(){
    cin >> n >> c;
    for(int i=1;i<=n;i++){
        cin >> a[i];
        maxi=max(maxi,a[i]);
    }
    sort(a,a+n);
    l=1;
    r=maxi-1;
    while(l<=r){
        mid=(l+r)/2;
        if(check(mid)){
        	l=mid+1;
		}else{
			r=mid-1;	
		}
    }
    cout << mid;
}