编译错误

#include<bits/stdc++.h>
using namespace std;
int n,m[207],a,b;
int main()
{
    cin>>n>>a>>b;
    for(int i=1;i<=n;i++)
        cin>>m[i];
    struct d
    {
        int st,fl;
    };
    queue<d>bf;
    d D;
    D.st=0;
    D.fl=a;
    bf.push(D);
    while(!bf.empty())
    {
        d nw=bf.front();
        bf.pop();
        if(nw.fl==b)
        {
            cout<<nw.st<<endl;
            return 0;
        }
        if(nw.fl>m[nw.fl])
        {
            d dd;
            dd.st=nw.st+1;
            dd.fl=nw.fl-m[nw.fl];
            bf.push(dd);
        }
        if(nw.fl<=n-m[nw.fl])
        {
            d dd;
            dd.st=nw.st+1;
            dd.fl=nw.fl+m[nw.fl];
            bf.push(dd);
        }
    }
    cout<<-1<<endl;
    return 0;
}