Common Subsequence

#include<cstdio>
#include<iostream>
#include<cmath>
#include<string>
#include<cstring>
#include<algorithm>
using namespace std;
int a[500][500];
int main()
{
    string s1,s2;
    while(cin>>s1>>s2)
    {
        int k1=s1.length();
        int k2=s2.length();
        memset(a,0,sizeof(a));
        for(int i=1; i<=k1; i++)
        {
            for(int j=1; j<=k2; j++)
            {
                if(s1[i-1]==s2[j-1])
                {
                    a[i%2][j]=a[(i-1)%2][j-1]+1;
                }
                else
                {
                    a[i%2][j]=max(a[(i-1)%2][j],a[i%2][j-1]);
                }
            }
        }
        printf("%d
",a[k1%2][k2]);
    }
    return 0;
}