Language: Java

import java.util.Scanner;

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        FastScanner fs = new FastScanner(System.in);

        int i = 0;
        int x;

        while(true) {
            if((x = Integer.parseInt(fs.next()))== 0) {
                break;
            }
                System.out.printf("Case %d: %d", ++i, x);
        }
    }
}



Compiler output:
Main.java:4: error: cannot find symbol
    private final InputStream in = System.in;
                  ^
  symbol:   class InputStream
  location: class FastScanner
Main.java:15: error: cannot find symbol
            } catch (IOException e) {
                     ^
  symbol:   class IOException
  location: class FastScanner
Main.java:29: error: cannot find symbol
        if (!hasNext()) throw new NoSuchElementException();
                                  ^
  symbol:   class NoSuchElementException
  location: class FastScanner
Main.java:39: error: cannot find symbol
        if (!hasNext()) throw new NoSuchElementException();
                                  ^
  symbol:   class NoSuchElementException
  location: class FastScanner
Main.java:66: error: constructor FastScanner in class FastScanner cannot be applied to given types;
        FastScanner fs = new FastScanner(System.in);
                         ^
  required: no arguments
  found:    InputStream
  reason: actual and formal argument lists differ in length
5 errors