# coding=utf-8
def firstnum(s):
    if s==None or len(s)==0:
        return -1
    alphapet={}#定义一个空字典
    alist=list(s)#将字符串放到列表里
    for item in alist:
        if item not in alphapet.keys():
            alphapet[item]=0#开始都不在字典里，所以初始个数设为0
        alphapet[item]+=1
    for item in alist:
        if alphapet[item]==1:
            return item
    return item
if __name__ == '__main__':
    print firstnum('aabccdf')