HDU-2046 骨牌铺方格

#include <iostream>
using namespace std;

int main(void)
{
    long long a, b, c;
    long long func(long long);
    
    while(cin >> a)
    {
        b = 1;  c = 2;
        
        for(int i = 2; i < a; i++)
        {
            c += b;
            b = c - b;
        }
        if(a == 1)
            a = b;
        else if(a == 2)
            a = c;
        else
            a = c;
        
        cout << a << endl;
    }
    
    return 0;
}