def main():
    n, m = [int(i) for i in input().split()]

    data = [[a for a in input()] for _ in range(n)]

    colors = set()
    for i in data:
        for j in i:
            colors.add(j)

    def voisins(i, j):
        col = data[i][j]
        v = [
            (i-1, j),
            (i+1, j),
            (i, j-1),
            (i, j+1)
        ]
        return [
            (a, b) for (a, b) in v
            if a >= 0 and b >= 0
            and a < n and b < m
            and data[a][b] == col
        ]

    vus = set()

    def parcours(i, j, pere=None):
        vus.add((i, j))
        vois = voisins(i, j)
        #print(f"voisins de {(i, j)}: {vois}")
        for v_ in vois:
            if v_ != pere:
                if v_ in vus:
                    return True
                vus.add(v_)
                if parcours(*v_, pere=(i, j)):
                    return True
        return False

    for i in range(n):
        for j in range(m):
            if (i, j) not in vus:
                # print(vus)
                if parcours(i, j):
                    return True
    return False


if main():
    print("Yes")
else:
    print("No")