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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.


package main

import (
	"fmt"
	"time"
)

func main() {
	start := time.Now()

	i, c, sum := [...]int{1, 1}, 0, 0
	for c < 4e6 {
		c = i[0] + i[1]
		i[0] = i[1]
		i[1] = c
		if c%2 == 0 {
			sum += c
		}
	}
	fmt.Println("Execution time: ", time.Since(start))
	fmt.Print(sum, "\n")
}

Execution time: 276ns

Answer: 4613732