求一个分数2/1, 3/2, 5/3, 8/5...前n项序列之和

 public static int FibonacciSum(int n) {
       if(n == 1) {
           return 2;
       }
       int sum = 0;
       int fenmu = 1, fenzi=2,sn =0 ;
       for(int i=1;i<=n; i++) {
           sum += fenzi/fenmu;
           sn = fenzi+fenmu;
           fenmu = fenzi;
           fenzi = sn;
       }
        return sum;
   }