考虑如下代码：

#include<bits/stdc++.h>
#define F(i,j,k) for(signed i=signed(j);i<=signed(k);i++)
#define endl '\n'
//#define int long long
using namespace std;
int a[1005],n;
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin>>n;
    a[1]=a[2]=1;
    F(i,3,n) a[i]=a[i-1]+a[i-2];//我想让gdb进入该循环，怎么办？
    cout<<a[n]<<endl;
    return 0;
}