哪错了，运行输出不对，玄关

#include<bits/stdc++.h>
using namespace std;
int n,m,a,x,a1=1,b1,a2,b2=1,a3,b3,t1=1,t2,c1,d1,y,ans; 
int read(){
	int ret=0,f=1;char ch=getchar();
	while (!isdigit(ch)){if (ch=='-')f=-f;ch=getchar();}
	while (isdigit(ch)) ret=(ret<<3)+(ret<<1)+(ch&15),ch=getchar();
	return ret*f;
}
int main(){
	cin>>a>>n>>m>>x;
	for(int i=3;i<=n;i++){
		c1=a2,d1=b2,a3=a1+a2,b3=b1+b2,a1=a2,b1=b2,a2=a3,b2=b3;
		t1=a3-c1,t2=b3-d1;
	}
	y=m-(c1*a)/d1;
	a1=a,a2=y,b2=y,b1=0,ans=a;
	for(int i=3;i<=x;i++){
		a3=a1+a2,b1=a2,a1=a2,a2=a3;
		ans+=a3-b1;
	}
	cout<<ans;
	return 0;
}