#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define REP(i,a,n) for(int i=(a); i<(int)(n); i++) #define rep(i,n) REP(i,0,n) #define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it) #define ALLOF(c) (c).begin(), (c).end() typedef long long ll; int main(){ vector v; v.push_back(4); v.push_back(3); double p = 4; double q = 3; REP(i,2,101){ double a = (19.0 * q - 12.0 * p)/4.0; v.push_back(a); p = q; q = a; } int N; cin >> N; cout << v[N] << endl; return 0; }