#!/usr/bin/env python3

import array
import itertools


def compute_levenshtein_distance(s1, s2):
    l1 = len(s1)
    l2 = len(s2)
    INF = 10 ** 6
    dp = [array.array("L", (INF for _ in range(l2 + 1)))
          for _ in range(l1 + 1)]
    for i1 in range(l1 + 1):
        dp[i1][0] = i1
    for i2 in range(l2 + 1):
        dp[0][i2] = i2
    for i1, i2 in itertools.product(range(1, l1 + 1), range(1, l2 + 1)):
        cost = s1[i1 - 1] != s2[i2 - 1]
        dp[i1][i2] = min(dp[i1 - 1][i2] + 1,  # insertion
                         dp[i1][i2 - 1] + 1,  # deletion
                         dp[i1 - 1][i2 - 1] + cost)  # replacement
    return dp[l1][l2]


def main():
    _ = input()
    print(compute_levenshtein_distance(input(), input()))


if __name__ == '__main__':
    main()