from collections import deque class Dinic: def __init__(self, N): self.N = N self.G = [[] for i in range(N)] def add_edge(self, fr, to, cap): forward = [to, cap, None] forward[2] = backward = [fr, 0, forward] self.G[fr].append(forward) self.G[to].append(backward) def add_multi_edge(self, v1, v2, cap1, cap2): edge1 = [v2, cap1, None] edge1[2] = edge2 = [v1, cap2, edge1] self.G[v1].append(edge1) self.G[v2].append(edge2) def bfs(self, s, t): self.level = level = [None]*self.N deq = deque([s]) level[s] = 0 G = self.G while deq: v = deq.popleft() lv = level[v] + 1 for w, cap, _ in G[v]: if cap and level[w] is None: level[w] = lv deq.append(w) return level[t] is not None def dfs(self, v, t, f): if v == t: return f level = self.level for e in self.it[v]: w, cap, rev = e if cap and level[v] < level[w]: d = self.dfs(w, t, min(f, cap)) if d: e[1] -= d rev[1] += d return d return 0 def flow(self, s, t): flow = 0 INF = 10**9 + 7 G = self.G while self.bfs(s, t): *self.it, = map(iter, self.G) f = INF while f: f = self.dfs(s, t, INF) flow += f return flow h, w = map(int, input().split()) assert (3 <= min(h, w) <= max(h, w) <= 800) h -= 2 a = [list(map(int, input().split())) for _ in range(h)] def ij(i, j, t): return (i*w+j)*2+t dinic = Dinic(h*w*2+2) inf = 10**10 s = h*w*2 for i in range(h): for j in range(w): if a[i][j] != -1: dinic.add_edge(ij(i, j, 0), ij(i, j, 1), a[i][j]) else: dinic.add_edge(ij(i, j, 0), ij(i, j, 1), inf) if i != h-1: dinic.add_edge(ij(i, j, 1), ij(i+1, j, 0), inf) dinic.add_edge(ij(i+1, j, 1), ij(i, j, 0), inf) if j != w-1: dinic.add_edge(ij(i, j, 1), ij(i, j+1, 0), inf) dinic.add_edge(ij(i, j+1, 1), ij(i, j, 0), inf) for j in range(w): dinic.add_edge(s, ij(0, j, 0), inf) dinic.add_edge(ij(h-1, j, 1), s+1, inf) ans = dinic.flow(s, s+1) if ans >= inf: print(-1) else: print(ans)