# UnionFind 参考は以下のサイト # https://note.nkmk.me/python-union-find/ from collections import defaultdict from decimal import Decimal class UnionFind(): def __init__(self, n): self.n = n self.parents = [-1] * n def find(self, x): if self.parents[x] < 0: return x else: self.parents[x] = self.find(self.parents[x]) return self.parents[x] def union(self, x, y): x = self.find(x) y = self.find(y) if x == y: return if self.parents[x] > self.parents[y]: x, y = y, x self.parents[x] += self.parents[y] self.parents[y] = x def size(self, x): return -self.parents[self.find(x)] def same(self, x, y): return self.find(x) == self.find(y) def members(self, x): root = self.find(x) return [i for i in range(self.n) if self.find(i) == root] def roots(self): return [i for i, x in enumerate(self.parents) if x < 0] def group_count(self): return len(self.roots()) def all_group_members(self): group_members = defaultdict(list) for member in range(self.n): group_members[self.find(member)].append(member) return group_members def __str__(self): return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items()) def is_ok(s): uf = UnionFind(N) hs = Decimal(s)**Decimal('0.5') for i,xyti in enumerate(XYT): for j,xytj in enumerate(XYT[i+1:],start=i+1): if not uf.same(i,j): if xyti[2]==xytj[2]: xi,yi,ti = xyti xj,yj,tj = xytj if (xi-xj)**2+(yi-yj)**2<=s: uf.union(i,j) else: if XY[i][j]<=hs: uf.union(i,j) return uf.same(0,N-1) def meguru_bisect(ng, ok): while (abs(ok - ng) > 1): mid = (ok + ng) // 2 if is_ok(mid): ok = mid else: ng = mid return ok N = int(input()) XYT = [list(map(int, input().split())) for _ in range(N)] D = [] for i in range(N): D.append(Decimal(XYT[i][0]**2+XYT[i][1]**2)**Decimal('0.5')) XY = [[0]*N for _ in range(N)] for i in range(N): for j in range(i+1,N): XY[i][j]=abs(D[i]-D[j]) print(meguru_bisect(-1,3200000001))