H,W = map(int,input().split())
S = [input().strip() for _ in range(H)]
dp = ["" for _ in range(W)]
dp[0] = S[0][0]
for j in range(1,W):
    dp[j] = dp[j-1]+S[0][j]
for i in range(1,H):
    dp[0] += S[i][0]
    for j in range(1,W):
        dp[j] = min(dp[j],dp[j-1])+S[i][j]
print(dp[W-1])