#include<bits/stdc++.h>
using namespace std;
const int N=10010;
int a[N];
int main()
{
	int n;
	cin>>n;
	a[1]=0,a[2]=1;
	for(int i=3;i<=n;i++)
	{
		a[i]=a[i-1]+a[i-2];
	}
	cout<<a[n];
	return 0;
}

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#include<bits/stdc++.h>
using namespace std;
int f(int x){
	if(x==1) return 0;
	if(x==2) return 1;
	return f(x-1)+f(x-2);
}
int main()
{
	int n;
	cin>>n;
	cout<<f(n);
	return 0;
}

有好心人发个题解码