14397.py

# 해변
import sys

input = sys.stdin.readline

N, M = map(int, input().split())

data = [input().rstrip() for _ in range(N)]

beach = 0

for i in range(N):
    for j in range(M - 1):
        if data[i][j] != data[i][j + 1]:
            beach += 1

    if i == N - 1:
        continue
    if i % 2 == 0:
        if data[i][0] != data[i + 1][0]:
            beach += 1
        for j in range(1, M):
            if data[i][j] != data[i + 1][j]:
                beach += 1
            if data[i][j] != data[i + 1][j - 1]:
                beach += 1
    else:
        if data[i][M - 1] != data[i + 1][M - 1]:
            beach += 1
        for j in range(M - 1):
            if data[i][j] != data[i + 1][j]:
                beach += 1
            if data[i][j] != data[i + 1][j + 1]:
                beach += 1
print(beach)