import java.io.*;
import java.math.*;

public class OffBase {
  public static final int MAX_RADIX = 40;
  public static final int MIN_RADIX = 2;

  public static final char[] digits = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 
    'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
    'U', 'V', 'W', 'X', 'Y', 'Z', '?', '~', '#', '|', 
  };

  String n1 = "";
  String n2 = "";
  String n3 = "";
  int minRadix, sign;
  int target = 1;
  char c;
  PrintStream out;
  public final int PLUS = 1;
  public final int MINUS = 2;

  public OffBase (){
    /* stdin/stdout */
    ACMIO in = ACMIO.getStdin();
    out = System.out;

    /* file I/O
    ACMIO in = new ACMIO("OffBase.in");
    out = null;
    try {
      out = new PrintStream(new FileOutputStream("OffBase.txt"));
    } catch (FileNotFoundException fnfe){
    }
    */
    
    int i = 1;
    while (!in.isEOF()){
      if (in.isEOLN()) {
	processEquation(i++, n1, n2, n3, sign, minRadix+1);
	n1 = ""; n2 = ""; n3 = "";
	sign = 0;
	minRadix = 0;
	target = 1;
	in.skipLine();
      } else if (target == 1) {
	c = in.charRead();
	if (c == '+') { sign = PLUS; target = 2; }
	else if (c == '-') { sign = MINUS; target = 2; }
	else { n1 = n1.concat(String.valueOf(c)); minRadix = setMax(minRadix, valueOf(c, OffBase.MAX_RADIX)); }
      } else if (target == 2) {
	c = in.charRead();
	if (c == '=') { target = 3; }
	else { n2 = n2.concat(String.valueOf(c)); minRadix = setMax(minRadix, valueOf(c, OffBase.MAX_RADIX)); }
      } else {
	c = in.charRead();
	n3 = n3.concat(String.valueOf(c)); 
	minRadix = setMax(minRadix, valueOf(c, OffBase.MAX_RADIX));
      }
    }
  }

  public int setMax(int currentMax, int potential){
    if (potential > currentMax) return potential;
    else return currentMax;
  }

  public static void main(String[] args) {
    new OffBase();
  }

  public void processEquation(int caseNum, String num1, String num2, String num3, int op, int minRadix){
    boolean abort = false;
    BigInteger dec1, dec2, dec3;
    for (int i = minRadix; i <= OffBase.MAX_RADIX; i++) {
      abort = false;
      dec1 = baseNToBase10(num1, i);
      dec2 = baseNToBase10(num2, i);
      dec3 = baseNToBase10(num3, i);
      if (dec1 == null || dec2 == null || dec3 == null) {
	abort = true;
      }
      if (op == PLUS && !abort) {
	if (dec1.add(dec2).equals(dec3)){
	  out.println("Case " + caseNum + ": minimum base is " + i);
	  return;
	}
      } else if (!abort){
	if (dec1.subtract(dec2).equals(dec3)){
	  out.println("Case " + caseNum + ": minimum base is " + i);
	  return;
	}
      }
    }
    out.println("Case " + caseNum + ": expression is invalid.");
  }

  public int valueOf(char c, int radix) {
    for (int i = 0; i < radix; i++) {
      if (c == OffBase.digits[i]) return i;
    }
    return -1;
  }

  public BigInteger baseNToBase10(String s, int radix) {
    BigInteger rdx = new BigInteger(String.valueOf(radix));
    if (s == null) {
       return null;
    }

    if (radix < OffBase.MIN_RADIX || radix > OffBase.MAX_RADIX){
       return null;
    }

     BigInteger result = new BigInteger("0");
    int digitValue;
    for(int i = 0; i < s.length(); i++){
      digitValue = valueOf(s.charAt(i), radix);
      if (digitValue == -1) return null;
      if (i != 0) {
	result = result.multiply(rdx);
      }
      result = result.add(new BigInteger(String.valueOf(digitValue)));
    }
    return result;
  }

}// OffBase