谁来帮帮我！

为什么它只输出0啊!

# include <bits/stdc++.h>
using namespace std;

int main (){
	int a,n,m,x;
	scanf("%d%d%d%d",&a,&n,&m,&x);
	int shu[21]={a,a},rs[21]={a,a},rx[21]={0,a};
	for (int i=3;i<=n;i++)
		rs[i] = rs[i-2]+rs[i-1];
	for (int i=3;i<=n;i++)
		shu[i] = rs[i-2]+rs[i-1]-shu[i-1];
	printf("%d",shu[x]);
	return 0;
}