import java.util.Scanner;

public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    }

    static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    }
} import java.util.Scanner; Scanner java.util public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    }

    static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    }
} Main public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    } main {
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    } Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int n = stdIn.nextInt(); n stdIn.nextInt() stdIn.nextInt stdIn int[] d = new int[n]; d new int[n] n for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            d[i] = stdIn.nextInt();
        } {
            d[i] = stdIn.nextInt();
        } d[i] = stdIn.nextInt() d[i] d i stdIn.nextInt() stdIn.nextInt stdIn quick_sort(d, 0, d.length-1) quick_sort d 0 d.length-1 d.length d d.length 1 if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        } n%2 == 1 n%2 n 2 1 {
            System.out.println(0);
        } System.out.println(0) System.out.println System.out System System.out 0 {
            System.out.println(d[n/2] - d[n/2-1]);
        } System.out.println(d[n/2] - d[n/2-1]) System.out.println System.out System System.out d[n/2] - d[n/2-1] d[n/2] d n/2 n 2 d[n/2-1] d n/2-1 n/2 n 2 1 String[] args args static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    } quick_sort {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    } if (left>=right) {
            return;
        } left>=right left right {
            return;
        } return; int p = d[(left+right)/2]; p d[(left+right)/2] d (left+right)/2 (left+right) left right 2 int l = left l left r = right r right tmp; tmp while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        } l<=r l r {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        } while(d[l] < p) { l++; } d[l] < p d[l] d l p { l++; } l++ l while(d[r] > p) { r--; } d[r] > p d[r] d r p { r--; } r-- r if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            } l<=r l r {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            } tmp = d[l] tmp d[l] d l d[l] = d[r] d[l] d l d[r] d r d[r] = tmp d[r] d r tmp l++ l r-- r quick_sort(d, left, r) quick_sort d left r quick_sort(d, l, right) quick_sort d l right int[] d d int left left int right right public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    }

    static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    }
} public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    }

    static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    }
} Main
import java.util.Scanner;

public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] d = new int[n];
        for(int i=0; i<n; i++){
            d[i] = stdIn.nextInt();
        }

        quick_sort(d, 0, d.length-1);

        if(n%2 == 1){
            System.out.println(0);
        }else{
            System.out.println(d[n/2] - d[n/2-1]);
        }
    }

    static void quick_sort(int[] d, int left, int right) {
        if (left>=right) {
            return;
        }
        int p = d[(left+right)/2];
        int l = left, r = right, tmp;
        while(l<=r) {
            while(d[l] < p) { l++; }
            while(d[r] > p) { r--; }
            if (l<=r) {
                tmp = d[l]; d[l] = d[r]; d[r] = tmp;
                l++; r--;
            }
        }
        quick_sort(d, left, r);  // ピボットより左側をクイックソート
        quick_sort(d, l, right); // ピボットより右側をクイックソート
    }
}