Java如何实现求出一个分数数列前20项的和

public class test20 {
  public static void main(String[] args) {
    float fm = 1f;
    float fz = 1f;
    float temp;
    float sum = 0f;
    for (int i=0;i<20;i++){
       temp = fm;
       fm = fz;
       fz = fz + temp;
       sum += fz/fm;
       //System.out.println(sum);
    }
    System.out.println(sum);
  }
}