#include <iostream> using namespace std; int main() { int a, n, m, x; cin >> a >> n >> m >> x; int p1 = a, p2 = a; int cur = a; if (x == 1) { cout << a << endl; return 0; } for (int i = 3; i < n; i++) { int p3 = p1 + p2; cur += p3 - p2; p2 = p3; p1 = p2; } if (x == n) { cur -= m; } if (cur < 0) { cout << "No answer." << endl; } else { cout << cur << endl; } return 0; }