题解

#include<bits/stdc++.h>
using namespace std;
int f[30],h[30],p[30]; 
int a,n,m,x,ans;
void checkx(int mul){
	if(x>=4) ans=(2+h[x-4])*a+h[x-3]*mul;
	else if(x==1||x==2) ans=a;
	else if(x==3) ans=2*a;
}
int main()
{
	f[1]=f[2]=h[1]=1; 
    h[2]=2;
	for(int i=3;i<=25;i++)
	{
		f[i]=f[i-1]+f[i-2];
		h[i]=h[i-1]+f[i];
	}
	
	cin>>a>>n>>m>>x;
	if(n>=5){
		int mul=0;
		mul=(m-(2+h[n-5])*a)/h[n-4];
		checkx(mul);
	}
	else checkx(0);
	cout<<ans<<endl;
	return 0;
}