public String omitChar(String str){
    	StringBuilder sb = new StringBuilder();
    	boolean hasOtherChar = false;
    	for(int i = 0; i < str.length(); i++){
    		if(isNum(str.charAt(i)) || (i == 0 && (str.charAt(i) == '+' || str.charAt(i) == '-')) ){
    			if(!hasOtherChar){
    				sb.append(str.charAt(i));
    			}
    		} else {
    			hasOtherChar = true;
    		}
    	}
    	return sb.toString();
    }