use strict;
use warnings;

my($len1, $len2) = split ' ', <STDIN>;
my @ar1 = split('', <STDIN>);
my @ar2 = split('', <STDIN>);
my @dist;
for(0..$len1){
  $dist[$_][0] = $_;
}
for(0..$len2){
  $dist[0][$_] = $_;
}

my $rep;
my $ref;
my @costs;
for my $i (1..$len1){
  for my $j (1..$len2){
    $rep = $ar1[$i-1] eq $ar2[$j-1] ? 0 : 1;
    @costs = ($dist[$i-1][$j] + 1, $dist[$i][$j-1] + 1, $dist[$i-1][$j-1] + $rep);
    $dist[$i][$j] = (sort {$a <=> $b} @costs)[0];
  }
}
print $dist[$len1][$len2];