public class Euler8 {
    static final String DIGITS = "73167176531330624919225119674426574742355349194934"
            + "96983520312774506326239578318016984801869478851843"
            + "85861560789112949495459501737958331952853208805511"
            + "12540698747158523863050715693290963295227443043557"
            + "66896648950445244523161731856403098711121722383113"
            + "62229893423380308135336276614282806444486645238749"
            + "30358907296290491560440772390713810515859307960866"
            + "70172427121883998797908792274921901699720888093776"
            + "65727333001053367881220235421809751254540594752243"
            + "52584907711670556013604839586446706324415722155397"
            + "53697817977846174064955149290862569321978468622482"
            + "83972241375657056057490261407972968652414535100474"
            + "82166370484403199890008895243450658541227588666881"
            + "16427171479924442928230863465674813919123162824586"
            + "17866458359124566529476545682848912883142607690042"
            + "24219022671055626321111109370544217506941658960408"
            + "07198403850962455444362981230987879927244284909188"
            + "84580156166097919133875499200524063689912560717606"
            + "05886116467109405077541002256983155200055935729725"
            + "71636269561882670428252483600823257530420752963450";

    static long maxAdjacentProduct(String digits, int window) {
        if (window <= 0 || window > digits.length())
            return 0;
        long best = 0;
        for (int i = 0; i + window <= digits.length(); i++) {
            long prod = 1;
            for (int j = 0; j < window; j++) {
                prod *= digits.charAt(i + j) - '0';
            }
            if (prod > best)
                best = prod;
        }
        return best;
    }

    static long solve(int window) {
        return maxAdjacentProduct(DIGITS, window);
    }

    public static void main(String[] args) {
        assert maxAdjacentProduct("123456789", 2) == 72 : "Checkpoint 1 failed";
        assert solve(4) == 5832 : "Checkpoint 2 failed";
        System.out.println(solve(13));
    }
}