from heapq import heapify, heappop, heappush

h, w = map(int, input().split())
S = [list(input()) for _ in range(h)]
Directions = [(1, 0), (0, 1)]

H = [(S[0][0], 0, 0)]
heapify(H)
while H:
    res, ci, cj = heappop(H)
    if ci == h - 1 and cj == w - 1:
        print(res)
        break
    for di, dj in Directions:
        ni = ci + di
        nj = cj + dj
        if ni < h and nj < w:
            heappush(H, (res + S[ni][nj], ni, nj))