class Solution {
public:
    string thousandSeparator(int n) {
        if(n==0)return "0";
        string s=to_string(n);
        reverse(s.begin(),s.end());
        string ans;
        int cnt=1;
        int i=0;//枚举原串每一位
        while(i<=s.size()-1){
            if(cnt%3==1&&cnt>3){
                ans+=".";
            }
            ans+=s[i];
            i++;
            cnt++;

        }
        reverse(ans.begin(),ans.end());
        return ans;
    }
};