【题解】【上海】【四铺地砖】

#include<bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
int i, n, f[100001];
int main() {
	cin.tie(0);
	cout.tie(0);
	cin >> n;
	f[1] = 1, f[2] = 3;
	for (i = 3; i <= n; ++i)
		f[i] = (f[i - 1] % MOD + 2 * f[i - 2] % MOD) % MOD;
	cout << f[n];
	return 0;
}