n,m=map(int,input().split())
S=input()
T=input()

DP=[[1<<30]*m for i in range(n)]

for i in range(m):
    if S[0]==T[i]:
        DP[0][i]=i
    else:
        DP[0][i]=i+1

for i in range(n):
    if S[i]==T[0]:
        DP[i][0]=i
    else:
        DP[i][0]=i+1

for i in range(n):
    for j in range(m):
        if S[i]==T[j]:
            if i-1>=0 and j-1>=0:
                DP[i][j]=min(DP[i-1][j-1],DP[i][j])
            if i-1>=0:
                DP[i][j]=min(DP[i-1][j]+1,DP[i][j])
            if j-1>=0:
                DP[i][j]=min(DP[i][j-1]+1,DP[i][j])
        else:
            if i-1>=0 and j-1>=0:
                DP[i][j]=min(DP[i-1][j-1]+1,DP[i][j])
            if i-1>=0:
                DP[i][j]=min(DP[i-1][j]+1,DP[i][j])
            if j-1>=0:
                DP[i][j]=min(DP[i][j-1]+1,DP[i][j])
            

print(DP[n-1][m-1])