H,W = map(int,input().split())
C = [input().strip() for _ in range(H)]
A = [["." for _ in range(2*W-1)] for _ in range(2*H-1)]
for i in range(H):
    for j in range(W):
        if C[i][j]=="#":
            A[2*i][2*j] = "#"
INFTY = 10**5
dp = [[INFTY for _ in range(2*W-1)] for _ in range(2*H-1)]
dp[0][0] = 0
for i in range(1,2*H-1):
    if A[i][0]=="#":continue
    if i%2==0:
        dp[i][0] = min(dp[i-1][0],dp[i-2][0])+1
    else:
        dp[i][0] = dp[i-1][0]+1
for j in range(1,2*W-1):
    if A[0][j]=="#":continue
    if j%2==0:
        dp[0][j] = min(dp[0][j-1],dp[0][j-2])+1
    else:
        dp[0][j] = dp[0][j-1]+1
for i in range(1,2*H-1):
    for j in range(1,2*W-1):
        if A[i][j]=="#":continue
        if i%2==0:
            dp[i][j] = min(dp[i-1][j],dp[i-2][j])+1
        else:
            dp[i][j] = dp[i-1][j]+1
        if j%2==0:
            dp[i][j] = min(dp[i][j],dp[i][j-1]+1,dp[i][j-2]+1)
        else:
            dp[i][j] = min(dp[i][j],dp[i][j-1]+1)
print(dp[2*H-2][2*W-2])