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

template <typename Key, typename Value>
class VectorMap {
    std::vector<Key> keys_;
    std::vector<Value> values_;

public:
    using K = Key;
    using V = Value;

    void insert(const Key& k, const Value& v) {
        keys_.emplace_back(k);
        values_.emplace_back(v);
    }

    Value& operator[](const Key& k);
    Value& at(const Key& k);
};

template <typename Key, typename Value>
Value& VectorMap<Key, Value>::operator[](const Key& k) {
    auto it = std::find(std::begin(keys_), std::end(keys_), k);
    if (it == std::end(keys_)) {
        keys_.emplace_back(k);
        values_.emplace_back(Value{});
        return values_.back();
    }
    auto dist = std::distance(keys_.begin(), it);
    return values_[dist];
}

template <typename Key, typename Value>
Value& VectorMap<Key, Value>::at(const Key& k) {
    auto it = std::find(std::begin(keys_), std::end(keys_), k);
    if (it == std::end(keys_)) {
        throw std::out_of_range("This key does not exist");
    }
    auto dist = std::distance(keys_.begin(), it);
    return values_[dist];
}