#include <stdio.h>
int main()
{
int a,b;
int data[102];
int next[102];
int count = 0;
int index = 0;
int len = 0;
while (scanf("%d%d",&a,&b) != EOF)
{
data[index] = a;
next[index] = b;
index++;
if (b != -1)
{
len++;
}
}
len--;
int i = 0;
printf("%d\n", len);
if (next[i] == 0)
{
return 0;
}
i = next[i];
while (next[i] != 0)
{
printf("%d ", data[i]);
i = next[i];
}
printf("%d\n", data[i]);
return 0;
}