N,M = map(int,input().split())
S = input()
T = input()
DP = [[10**5]*(M+1) for _ in range(N+1)]
DP[0][0]=0
for i in range(N):
    for j in range(M):
        if S[i]==T[j]:
            DP[i+1][j+1]=min(DP[i+1][j+1],DP[i][j])
        else:
            DP[i+1][j+1]=min(DP[i+1][j+1],DP[i][j]+1)
        DP[i+1][j]=min(DP[i+1][j],DP[i][j]+1)
        DP[i][j+1]=min(DP[i][j+1],DP[i][j]+1)

print(min(DP[N][M],DP[N-1][M]+1,DP[N][M-1]+1))