h,w = map(int,input().split())
s = [input() for i in range(h)]
dp = [""]*(w)
for i in range(h):
  new = [""]*w
  for j in range(w):
    if i == 0 and j == 0:
      new[j] = s[0][0]
    elif i == 0:
      new[j] = new[j-1] + s[i][j]
    elif j == 0:
      new[j] = dp[j] + s[i][j]
    else:
      new[j] = min(new[j-1], dp[j]) + s[i][j]
  dp = new
print(new[-1])