func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, i, j, k, p = 1000000007;   int A[10], B[10];   int main() {     cin >> n;     A[0] = 1;     for (i = 1; i <= n; i++) {       for (j = 0; j <= 3; j++)         for (k = 0; k <= 3; k++) {           if (j == k) continue;           B[j] = (B[j] + A[k]) % p;         }       for (j = 0; j <= 3; j++) {         A[j] = B[j];         B[j] = 0;       }     }     cout << A[0] << endl;     return 0;   }   