为什么只有20分，大佬们看看

#include <iostream>
using namespace std;
int n;
const int N = 150;
int a[N],b[N],c[N];
void jf(){
    int x = 0;
    for(int i = 1;i <= 150;i++){
        c[i] = a[i] + b[i] + x;
        x = c[i] / 10;
        c[i] %= 10;
    }
}
int main(){
    scanf("%d",&n);
    if(n < 3){
        cout << n;
    }else{
        a[1] = 1;
        b[1] = 2;
        for(int i = 3;i <= n;i++){
            jf();
            for(int j = 1;j <= 150;j++){
                a[j] = b[j];
            }
            for(int j = 1;j <= 150;j++){
                b[j] = c[j];
            }
        }
        int index = 150;
        while(index > 1 && c[index] == 0){
            index--;
        }
        for(int i = index;i > 0;i--){
            printf("%d",b[i]);
        }
    }
    
    return 0;
}