/**
 *   斐波那契数列
 */
export default function fibonacci(n){
  if(n <= 2){
    return 1;
  }
  let n1 = 1, n2 = 1, sn = 0;
  for(let i = 0; i < n - 2; i ++){
    sn = n1 + n2;
    n1 = n2;
    n2 = sn;
  }
  return sn;
}
