import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class SafeHouses {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        int n = Integer.parseInt(scanner.nextLine());

        String[] numbersAsString = scanner.nextLine().split(" ");
//        int[] positions = new int[numbersAsString.length];
        List<Integer> positionsList = new ArrayList<>();

        for (int i = 0; i < numbersAsString.length; i++) {
//            positions [i] = Integer.parseInt(numbersAsString[i]);
            positionsList.add(Integer.parseInt(numbersAsString[i]));
        }

        int maxDistance = 0;

        if(n==positionsList.size()){
            System.out.println(maxDistance);
            return;
        }

        if(positionsList.size()>1){
            Collections.sort(positionsList);
        }else{
            if(positionsList.get(0)>=(n*1.0/2)){
                maxDistance = positionsList.get(0);
            }else{
                maxDistance = (n -1) - positionsList.get(0);
            }
        }

        int distance = 0;
       // int nextPosition = 0;

        for (int i = 0; i < positionsList.size()-1; i++) {
             int nextPosition = positionsList.get(i+1);
             int difference = nextPosition - positionsList.get(i);

             if(i!=0){
                 if(i+1==positionsList.size()-1){
                     if((difference * 1.0/2)> ((n-1)- nextPosition)){
                        if(difference%2==0){
                            distance = difference/2;
                         }else{
                            distance = (difference - 1)/2;
                        }
                     }else{
                         distance = (n-1)- nextPosition;
                     }
             }else{
                     if(difference%2==0){
                         distance = difference/2;
                     }else{
                         distance = (difference - 1)/2;
                     }
                 }
             }else{
                 if((difference * 1.0/2)>positionsList.get(i)){
                     if(i+1==positionsList.size()-1){
                         if((difference * 1.0/2)> ((n-1)- nextPosition)){
                             if(difference%2==0){
                                 distance = difference/2;
                             }else{
                                 distance = (difference - 1)/2;
                             }
                         }else{
                             distance = (n-1)- nextPosition;
                         }
                     }else{
                         if(difference%2==0){
                             distance = difference/2;
                         }else{
                             distance = (difference - 1)/2;
                         }
                     }
                 }else{
                     distance = positionsList.get(i);
                 }
             }

                if(distance>maxDistance){
                    maxDistance = distance;
                }


        }

        System.out.println(maxDistance);
    }
}