#include<bits/stdc++.h> using namespace std; int n, a, m, x; int cz[21];// cz[i]代表第i站的总人数 int sc[21];// sc[i]代表第i站的上车人数 int xc[21];// xc[i]代表第i站的下车人数 int main() { cin >> a >> n >> m >> x; sc[1] = a; xc[1] = 0; cz[1] = 0 + sc[1] - xc[1]; for(int k = 0; ; k++) { sc[2] = k; xc[2] = k; cz[2] = cz[1] + sc[2] - xc[2]; for(int z = 3; z <= n-1; z++){ sc[z] = sc[z-1] + sc[z-2]; xc[z] = sc[z-1]; cz[z] = cz[z-1] + sc[z]-xc[z]; } if(cz[n-1] == m){ cout << cz[x]; return 0; } if(cz[n-1] > m){ cout << "No answer."; return 0; } } return 0; }