2070 Fibbonacci Number

#include<iostream>using namespace std;int main(){int n;while (cin >> n){if (n == -1)break;__int64 a[51];a[0] = 0, a[1] = 1;for (int i = 2; i <= n; ++i)a[i] = a[i - 1] + a[i - 2];cout << a[n] << endl;}return 0;}