#include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define ll long long int #define rep(i,n) for( int i = 0; i < n; i++ ) #define rrep(i,n) for( int i = n; i >= 0; i-- ) #define REP(i,s,t) for( int i = s; i <= t; i++ ) #define RREP(i,s,t) for( int i = s; i >= t; i-- ) #define dump(x) cerr << #x << " = " << (x) << endl; #define INF 2000000000 #define mod 1000000007 #define INF2 1000000000000000000 #define int long long signed main(void) { cin.tie(0); ios::sync_with_stdio(false); int N; cin >> N; double A[101]; A[0] = 4; A[1] = 3; REP(i, 2, N) { A[i] = (19 * A[i - 1] - 12 * A[i - 2]) / 4; } cout << fixed; cout << setprecision(10) << A[N] << endl; return 0; }