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

S_A = 0
S_B = 0
for i in range(N):
    if S[i] == "A":
        S_A += 1
    else:
        S_B += 1
        
T_A = 0
T_B = 0
for i in range(M):
    if T[i] == "A":
        T_A += 1
    else:
        T_B += 1
        
print(min(S_A, T_A) + min(S_B, T_B))