# Each new term in the Fibonacci sequence is generated by adding the previous two terms. 
# By starting with 1 and 2, the first 10 terms will be:
# 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
#
# By considering the terms in the Fibonacci sequence whose values do not exceed four million, 
# find the sum of the even-valued terms.

fib = 3
fib_1 = 2
fib_2 = 1
s = 2

while fib < 4000000:
	if fib % 2 == 0:
		s += fib
	fib_2, fib_1, fib = fib_1, fib, fib + fib_1

print(s)