O(n²)
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstdio>
#include<vector>
#include<queue>
#include<string.h>
#include<set>
#include<map>
using namespace std;
const int maxn =1e6+10;
char a[maxn];
char b[maxn];
int f[1006][1006];
int main()
{
int n,m;
cin >> n >> m;
cin >> a+1;
cin >> b+1;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++)
{
f[i][j]=max(f[i-1][j],f[i][j-1]);
if(a[i]==b[j])
f[i][j]=max(f[i-1][j-1]+1,f[i][j]);
}
}
cout << f[n][m] << endl;
return 0;
}