#include<iostream> using namespace std; int a,n,m,x; int sha[20],zong[20],xia[20]; int main(){ cin >> a >> n >> m >>x; sha[1]=a;xia[1]=0;zong[1]=a; int k=0; while(true){ sha[2]=k;xia[2]=k;zong[2]=a; for(int i=3;i<=n-1;i++){ sha[i]=sha[i-1]+sha[i-2]; xia[i]=sha[i-1]; zong[i]=zong[i-1]+sha[i]-xia[i]; }if(zong[n-1]==m){ cout << zong[x]; break; } else{ k++; }if(zong[n-1]>m){ cout << "No answer."; return 0; } } return 0; }