class Solution {
public:
    int rectCover(int n) {
        if (n == 0 || n == 1 || n == 2) return n;
        int a = 1;
        int b = 2;
        int sum;
        for (int i = 3; i <= n; ++i) {
            sum = a + b;
            a = b;
            b = sum;
        }
        return sum;
    }
};