int fill() {
        // System.out.println(s1);
        // System.out.println(s1.length());
        // System.out.println(s2);
        // System.out.println(s2.length());

        //bottom up dynamic programing
        for (int i = 1; i < s1.length(); i++) {
            for (int j = 1; j < s2.length(); j++) {
                int max = D[i - 1][j - 1] + score(i, j);
                int left = D[i][j - 1] + w;
                int up = D[i - 1][j] + w;

                if (max < up) {
                    max = up + w;
                }

                if (max < left) {
                    max = left + w;
                }

                D[i][j] = max;
            }
        }
        return D[s1.length() - 1][s2.length() - 1];