usaco Riding the Fences

/*
ID: guo geer
PROG: fence
LANG: C++
*/
#include<iostream>
#include<cstring>
#include<cmath>
#include<fstream>
using namespace std;

int a[510][510],b[510],path[1029],stack[1029];

int getMin(int s[])
{
    for(int i=1; i<=500; i++)
    if(s[i] > 0) return i;
    return -1;
}

int main()
{
    ifstream fin("fence.in");
    ofstream fout("fence.out");
    
    int F;
    while(fin>>F)
    {
        memset(a, 0, sizeof(a));
        memset(b, 0, sizeof(b));
        
        int x,y,st=510;
        for(int i=0; i<F; i++)
        {
                fin>>x>>y;
                st=min(st,min(x,y));
                a[x][y] ++;
                a[y][x] ++;
                b[x] ++;
                b[y] ++;
        }
        for(int i=1; i<=500; i++) if(b[i]%2 == 1){st = i; break;}
        
        int p = 0, top=-1;
        stack[++ top] = st;

        while(top != -1)
        {
              st = stack[top];

              if(b[st] == 0) path[p ++] = st, top --;
              while(b[st] > 0)
              {
                     int tt = getMin(a[st]);                     
                     b[st] --;
                     b[tt] --;
 
                     a[st][tt] --;
                     a[tt][st] --;                 
                     st = tt;
                     stack[++top] = st;
              }
        }
        for(int i=F; i>=0; i--) fout<<path[i]<<endl;
    }
    return 0;
}