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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Day 1
Step1:  Question 1
Find the two entries that sum to 2020 and then multiply those two numbers together.
Step2:  Question 2
What is the product of the three entries that sum to 2020?
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Python Code:
input_f = './input.txt'
# Read expenses
expenses = set()
with open(input_f, 'r') as fd: 
    for line in fd: 
        expenses.add(int(line.strip()))
Explanation: Day 1
End of explanation
# Find 2 expenses that add up to 2020 and get their product
stop = 0
for exp1 in expenses: 
    for exp2 in expenses: 
        if exp1 + exp2 == 2020: 
            print(exp1, exp2, exp1 * exp2)
Explanation: Question 1
Find the two entries that sum to 2020 and then multiply those two numbers together.
End of explanation
# First try, not very nice
stop = 0
for exp1 in expenses: 
    for exp2 in expenses:
        for exp3 in expenses: 
            if exp1 + exp2 + exp3 == 2020: 
                print(exp1, exp2, exp3, exp1 * exp2 * exp3)
                stop = 1
def evaluate_3(a, b, c): 
    if a + b + c == 2020: 
        return a * b * c
    else: 
        return 0
# Second option (would also apply to question 1)
solution = 0
for exp1 in expenses: 
    for exp2 in expenses:
        for exp3 in expenses: 
            solution = evaluate_3(exp1, exp2, exp3)
            if solution != 0: 
                break
        if solution != 0: 
            break
    if solution != 0: 
        break
print(solution)
Explanation: Question 2
What is the product of the three entries that sum to 2020?
End of explanation
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