[백준]10870-피보나치 수 5 (설명X)

#include <iostream>
using namespace std;
 
int main()
{
    int input;
    cin >> input;
    int arg1 = 0, arg2 = 1, sum = 0;
    switch (input)
    {
    case 0:
        cout << 0;
        break;
    case 1:
        cout << 1;
        break;
    default:
        for (size_t i = 1; i < input; i++)
        {
            sum = arg1 + arg2;
            arg1 = arg2;
            arg2 = sum;
        }
        cout << sum;
        break;
    }
    return 0;
}