public static String blowup(String str) {

		 int at = 0;
		 StringBuilder result = new StringBuilder();
		 for (;at < str.length(); at++) {
			 char ch = str.charAt(at);

			 if (Character.isDigit(ch)) {
				 int num = ch - 48;
				 while((at+1) != str.length() && num > 0) {
					 result.append(str.charAt(at+1));
					 num--;
				 }
			 } else {
				 result.append(ch);
			 }

		 }
		 return result.toString();
	}