#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> v { 1, 2, 3, 4 };
    auto it = std::find(begin(v), end(v), 2);
    v.insert(it, { -1, -2, -3 });
    for (auto i: v) std::cout << i << ' ';
    std::cout << std::endl;
}