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  1. Buy Two Chocolates

You are given an array of integers calories where calories[i] represents the number of calories in the i-th type of chocolate. You want to eat exactly two chocolates such that no other chocolate is eaten before them. If you can do this, return the minimum possible calories you will consume. If it is not possible to buy exactly two chocolates, return -1.

Example 1:

Input: calories = [1, 2, 3]
Output: 3 
Explanation: You can buy the first and second chocolates which have a total of 1 + 2 = 3 calories.

**Example 2:**
```python
Input: calories = [1]
Output: -1 
Explanation: You cannot buy exactly two chocolates.

### Clarifying Questions
1. **Can the array be empty?**
   - No, the problem guarantees that there will be at least one integer in the array.
2. **Can the array contain only one chocolate?**
   - Yes, and in such cases, you should return -1 as purchasing exactly two chocolates is not possible.
3. **Are the calories values always positive integers?**
   - Yes, the calories are always positive integers.

### Strategy
To solve this problem, you can follow these steps:
1. **Edge Case Handling:** If the length of the `calories` list is less than 2, return -1 immediately since it's impossible to buy two chocolates.
2. **Sorting Approach:** Sort the list of calories. The first two elements in this sorted list will be the two chocolates with the smallest calorie counts (i.e., the minimum calories you will consume will be the sum of these two numbers).
3. **Summation:** Return the sum of the two smallest elements.

This approach sorts the array first, which ensures that the two smallest elements are considered. This is efficient for small to moderate size inputs.

### Time Complexity
- **Sorting:** \(O(n \log n)\) where \(n\) is the length of the `calories` list.
- **Summation of first two elements:** \(O(1)\)

Overall, the time complexity is dominated by the sorting step, so it is \(O(n \log n)\).

### Code
Let's put this strategy into the code:

```python
from typing import List

def buy_two_chocolates(calories: List[int]) -> int:
    if len(calories) < 2:
        return -1
    
    # Sort the calories to find the two chocolates with minimum calories
    calories.sort()
    
    # The minimum calories will be the sum of the first two elements
    return calories[0] + calories[1]

# Example usages
print(buy_two_chocolates([1, 2, 3]))  # Output: 3
print(buy_two_chocolates([1]))         # Output: -1

This code first checks if it’s possible to buy two chocolates (array length >= 2), sorts the list of calories, and returns the sum of the two smallest values.

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