import java.util.Scanner

object Problem225 {

  def proc(n: Int, m: Int, S: String, T: String): Int = {
    val dp = Array.fill(n + 1, m + 1)(0)
    (0 to S.length) foreach (i => dp(i)(0) = i)
    (0 to T.length) foreach (i => dp(0)(i) = i)

    for (i <- 1 to S.length; j <- 1 to T.length) {
      val cost = if (S(i - 1) == T(j - 1)) 0 else 1
      dp(i)(j) = Seq(dp(i - 1)(j) + 1, dp(i)(j - 1) + 1, dp(i - 1)(j - 1) + cost).min
    }

    dp(S.length)(T.length)
  }

  def main(args: Array[String]) {
    val sc = new Scanner(System.in)
    val (n, m) = (sc.nextInt(), sc.nextInt())
    val S = sc.next()
    val T = sc.next()

    val result = proc(n, m, S, T)
    println(result)
  }
}