C++ :

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
int weishenmeCEle[3005];
int main()
{
    //freopen("D input.txt","r",stdin);
    //freopen("D output.txt","w",stdout);
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        memset(weishenmeCEle,0,sizeof(weishenmeCEle));
        for(int i=1;i<n;i++)
            weishenmeCEle[i]=i+1;
        for(int i=n+1;i<=2*n;i++)
        {
            int l,r;
            scanf("%d%d",&l,&r);
            weishenmeCEle[l]=i;
            weishenmeCEle[i]=r;
        }
        int p=1;
        while(p)
        {
            printf("%d ",p);
            p=weishenmeCEle[p];
        }
        printf("\n");
    }
}