fibonacci中的偶数值项sum，限制为400万

function fibonacci(n) {
  if (n <= 1) {
    return n;
  }
  return fibonacci(n - 1) + fibonacci(n - 2);
}

function calculateSum(limit) {
  let sum = 0;
  let n = 1;
  let fib = fibonacci(n);
  
  while (fib <= limit) {
    if (fib % 2 === 0) {
      sum += fib;
    }
    n++;
    fib = fibonacci(n);
  }
  
  return sum;
}

const limit = 4000000;
const sum = calculateSum(limit);

console.log('The sum of even-valued Fibonacci terms not exceeding', limit, 'is', sum);