C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int G[510][510];
int n, f;
int path[2000];
int degree[510];
int index;

void dfs(int u){
for(int v = 1;v <= n; v++){
    if(G[u][v]){
        G[u][v]--;
        G[v][u]--;
        dfs(v);
    }
}
path[index++] = u;
}

int main()
{
    while(scanf("%d",&f) != EOF){
        memset(G,0,sizeof(G));
        memset(path,0,sizeof(path));
        memset(degree,0,sizeof(degree));
        n = 0;
        for(int i = 0;i < f; i++){
            int a, b;
            scanf("%d%d",&a,&b);
            G[a][b]++;
            G[b][a]++;
            degree[a]++;
            degree[b]++;
            int temp = a < b ? b : a;
            n = n < temp ? temp : n;
        }
        int st = 1;
        for(int i = 1;i <= n; i++){
            if((degree[i] & 1) == 1){
                st = i;
                break;
            }
        }
        index = 0;
        dfs(st);
        for(int i = index-1;i>=0;i--){
            printf("%d\n",path[i]);
        }
    }
    return 0;
}

C++ :

#include<iostream> 
#define MAX 1024
using namespace std;
int g[MAX][MAX]={0};
int d[MAX]={0};
int r[MAX]={0};
int n=0,e,a,b,m=0;
void in();
void find(int i);
void out();
int main()
{
	in();
	for(int i=1;i<n+1;i++)
	{
		if(d[i]%2==1)
		{
			find(i);
			out();
			return 0;
		}
	}
	find(1);
	out();
	return 0;
}
void in() {
	cin>>e;
	for(int i=1;i<e+1;i++)
	{
		cin>>a>>b;
		m=max(a,b);
		n=max(n,m);
		g[a][b]++;
		g[b][a]++;
		d[a]++;
		d[b]++;
	}
}
void find(int i) {
	for(int j=1;j<n+1;j++)
	{
		if(g[i][j]>0)
		{
			g[i][j]--;
			g[j][i]--;
			find(j);
		}
	}
	r[++r[0]]=i;
}
void out() {
	for(int i=r[0];i>0;i--)
	{
		cout<<r[i]<<endl;
	}
}