a, b = map(int,input().split())
road = []
for i in range(a):
    row = list(map(int,input().split()))
    road.append(row)
min_val = 10000000
start_x = start_y = 0
for i in range(a):
    for j in range(b):
        if road[i][j] < min_val:
            min_val = road[i][j]
            start_x = i
            start_y = j
visited = [[False]*b for _ in range(a)]
visited[start_x][start_y] = True
total = road[start_x][start_y]
x = start_x
y = start_y
dx = [-1, 1, 0, 0]
dy = [0, 0, -1, 1]
while True:
    min_next = 10000000
    next_x = -1
    next_y = -1
    for i in range(4):
        nx = x + dx[i]
        ny = y + dy[i]
        if 0 <= nx < a and 0 <= ny < b:
            if not visited[nx][ny] and road[nx][ny] < min_next:
                min_next = road[nx][ny]
                next_x = nx
                next_y = ny
    if next_x == -1:
        break
    x = next_x
    y = next_y
    visited[x][y] = True
    total += road[x][y]
print(total)