What does this C++ snippet output?

1#include <iostream>
2#include <vector>
3int main() {
4    std::vector<int> v = {1, 2, 3, 4};
5    v.insert(v.begin() + 2, 99);
6    for (int x : v) std::cout << x << " ";
7    std::cout << "\n";
8}