#include <iostream>
#include <cstdio>
#include <cstring>
#include <stack>
#include <map>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
const int N = (1<<14);

int  n , m , st[N<<1] ,top , ans[N<<1] , tail ;
int eh[N] , et[N<<2] , nxt[N<<2] , tot ;
bool mark[N<<2];

struct node
{
    int x , y ;
}  key[N<<1] , door[N<<1];

void init()
{
    tot = 0 ;
    memset( eh , -1 , sizeof eh );
    memset( mark ,false , sizeof mark );
}

void addedge( int u , int v )
{
    et[tot] = v , nxt[tot] = eh[u] , eh[u] = tot++ ;
    et[tot] = u , nxt[tot] = eh[v] , eh[v] = tot++ ;
}

bool dfs( int u )
{
    if( mark[u] ) return true;
    if( mark[u^1] ) return false ;
    mark[u] = true ;
    st[top++] = u ;
    for( int i = eh[u] ; ~i ; i = nxt[i] ){
        int v = et[i];
        if( !dfs(v^1) )  return false;
    }
    return true;
}

bool solve()
{
    tail = 0 ;
    for( int i = 0 ; i < 2 * n ; i += 2 ){
        if( !mark[i] && !mark[i+1] ) {
            top = 0 ;
            if( !dfs(i) ){
                while( top > 0 ) mark[ st[--top] ] = false ;
                if( !dfs(i+1) ) return false;
            }
        }
        if( mark[i] )
            ans[tail++] = i + 1 ;
        else
            ans[tail++] = i + 2 ;
    }
    return true;
}

void run()
{
    int x, y ;
    init();
    for( int i = 0 ; i < m ; ++i ){
        scanf("%d%d",&x,&y);
        x-- , y -- ;
        addedge(x,y) ;
    }
    if( !solve() )puts("NIE");
    else {
        for( int i = 0 ; i < tail ;++i )
            printf("%d\n",ans[i]);

    }
}

int main()
{
    #ifdef LOCAL
        freopen("in.txt","r",stdin);
    #endif // LOCAL
    while( ~scanf("%d%d",&n,&m) ) run();
}