Thousand Separator Problem & Solution

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
#pragma GCC target("avx,avx2,fma")

static const int _=[](){ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

class Solution {
public:
  string thousandSeparator(int n) {
    string s = to_string(n);

    int i = 3;
    while (i < s.size()) {
      s.insert(s.size() - i, ".");
      i += 4;
    }
    
    return s;
  }
};