import java.math.BigInteger;
import java.util.*;

public class IBAN {
    static final Map<String, Integer> isoPairs;

    static final String iso = "AL28 AD24 AT20 AZ28 BE16 BH22 BA20 BR29 BG22 "
            + "HR21 CY28 CZ24 DK18 DO28 EE20 FO18 FI18 FR27 GE22 DE22 GI23 "
            + "GL18 GT28 HU28 IS26 IE22 IL23 IT27 KZ20 KW30 LV21 LB28 LI21 "
            + "LT20 LU20 MK19 MT31 MR27 MU30 MC27 MD24 ME22 NL18 NO15 PK24 "
            + "PS29 PL28 PT25 RO24 SM27 SA24 RS22 SK24 SI19 ES24 SE24 CH21 "
            + "TN24 TR26 AE23 GB22 VG24 GR27 CR21";

    static {
        isoPairs = new HashMap<>();
        for (String p : iso.split(" "))
            isoPairs.put(p.substring(0, 2), Integer.parseInt(p.substring(2)));
    }

    public static void main(String[] args) {
        for (String iban : new String[]{"GB82 WEST 1234 5698 7654 32",
            "GB82 TEST 1234 5698 7654 32",
            "GB81 WEST 1234 5698 7654 32",
            "SA03 8000 0000 6080 1016 7519",
            "CH93 0076 2011 6238 5295 7"})
            System.out.printf("%s is valid: %s%n%n", iban, validateIBAN(iban));
    }

    static boolean validateIBAN(String iban) {
        iban = iban.replaceAll("\\s", "").toUpperCase();

        int len = iban.length();

        if (len < 4 || isoPairs.get(iban.substring(0, 2)) != len)
            return false;

        iban = iban.substring(4) + iban.substring(0, 4);

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < len; i++)
            sb.append(Character.digit(iban.charAt(i), 36));

        BigInteger bigInt = new BigInteger(sb.toString());

        return bigInt.mod(new BigInteger("97")).intValue() == 1;
    }
}