1. #include<stdio.h>
    2. #include<algorithm>
    3. #include<vector>
    4. using namespace std;
    6. vector<int> fn(50, -1);
    8. int F(int n){
    9.     if(n == 0||n == 1) return n;
    10.     if(fn[n] != -1) return fn[n];
    11.     else{
    12.         fn[n] = F(n - 1) + F(n - 2);
    13.         return fn[n];
    14.     }
    15. }
    17. int main(){
    18.     int num;
    19.     scanf("%d", &num);
    20.     printf("%d", F(num));
    21.     return 0;
    22. }