View Code of Problem 3870

#include <bits/stdc++.h>
#define per(i,a,b) for(int i=a;i<b;i++)
using namespace std;

const int maxn(1e4 + 7);
int n;
long long x[maxn], y[maxn];
double ans;
int dex;

int main() {

	while (cin >> n) {
		if (n == 3) {
			n = 3;
		}
		per(_, 1, n + 1) {
			cin >> x[_] >> y[_];
		}
		dex = 0;
		per(i, 1, n + 1) {
			ans = 0;
			per(j, 1, n + 1) {
				if (i != j) {
					if (ans == 0) {
						ans = sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]));
					}
					else if (sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j])) != ans) {
						break;
					}
					else {
						if (j == n || (i == n && j == n - 1)) {
							dex = i;
							break;
						}
					}
				}
			}
			if (dex) {
				break;
			}
		}
		if (!dex) {
			dex = -1;
		}
		cout << dex << endl;
	}
}