#include<stdio.h>
#include<iostream>

using namespace std;
int a,b,n,m,g[1000][1000];
int _max = -1000;
int main()
{
scanf("%d %d",&n,&m);

for(int i = 1;i<=m;i++)
{

                scanf("%d %d",&a,&b);
                g[a][b]=1;
                g[b][a]=1;
}


for(int k = 1;k<=2*n;k++)
{
        for(int l = 1;l<=2*n;l++)
        {
           if(k==l){continue;}
           else if(g[k][l]==1)
           {
           g[k][l]=2;
           g[k][l]=2;
           }
        }
}

for(int k = 1;k<=2*n;k++)
{
        for(int l = 1;l<=2*n;l++)
        {
           if(k==l){continue;}
           else if(g[k][l]==0)
           {
           g[k][l]=1;
           g[k][l]=1;
           }
        }
}

int key = 0;
for(int k = 1;k<=2*n;k++)
{
        for(int l = 1;l<=2*n;l++)
        {
          if(key>=2){return 0;}
          else if(k==l){continue;}
          else if(g[k][l]==1)
          {
                printf("%d %d\n",k,l);
                key++;
          }
        }

}

printf("IMPOSSIBLE");
}