poj3579

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define MAX_N 100010

typedef long long LL;

int N;
int x[MAX_N];

bool C(int m){
        LL total = (LL) N * (N - 1) / 2;
        LL num = 0;
        
        for(int i = 0;i < N; i++){
                num += (x+N) - lower_bound(x + i + 1, x + N, x[i] + m);
        }
        
        return total - num <= (total - 1) / 2;
        
}
int solve(){
        sort(x, x + N);
        int lb = 0, ub = 1000000000;
        while(ub - lb > 1){
                int mid = (ub + lb) / 2;
                if(C(mid)) lb = mid;
                else ub = mid;
        }
        return lb;
}

int main(){
        while(scanf("%d", &N) != EOF){
                for(int i = 0;i < N; i++)
                        scanf("%d", &x[i]);
                int ans = solve();

                printf("%d\n", ans);
        }
        return 0;
}