没有输入，也没有输出

#include<bits/stdc++.h>
using namespace std;
struct note{
    string s;
    int step;
}que[2510];
int head=0,n,tail=1;
string ss,fs,sa[8],sb[8];
int main()
{
    int i,m,flag=0;
    n=1;
    cin>>ss>>fs;
    while(cin>>sa[n]>>sb[n])
    n++;
    n--;
    que[0].s=ss;
    que[0].step=0;
    if(ss==fs)
    {
        cout<<"NO ANSWER!"<<endl;
        return 0;
    }
    while(head<tail)
    {
        for(i=1;i<=n;i++)
        {
            m=que[head].s.find(sa[i]);
            if(m==-1)continue;
            if(que[head].step==10)
            {
                flag=1;
                break;
            }
            que[tail].s=que[head].s;
            que[tail].s.replace(m,sa[i].size(),sb[i]);
            que[tail].step=que[head].step+1;
            if(que[tail].s==fs)
            {
                cout<<que[tail].step<<endl;
                flag=1;
                break;
                tail++;
            }
        }
        if(flag==1)break;
        head++;
    }
    return 0;
}