#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <string>
#include <stack>
#include <vector>
#include <algorithm>
struct edge{
    int st;
    int to;
    int next;
};
const int inf = 0x3f3f3f;
const int MAXN  = 8e3+10;
const int MAXNN = 2e4+10;

using namespace std;
int first[2*MAXN];
edge e[2*MAXNN];
int color[2*MAXN];
int S[2*MAXN];
int top,l;
int n,m;
int flag;

void init(){
    l = 0;
    memset(first,-1,sizeof(first));
    memset(color,0,sizeof(color));
    flag= 1;
}

void addEdge(int u,int v){
    e[l].st = u;
    e[l].to = v;
    e[l].next = first[u];
    first[u] = l++;
}

int dfs(int v){
    if(color[v]==2)return 0;    //如果深搜到已经染色为2的，不成立
    if(color[v]==1)return 1;
    color[v] = 1;    //本节点染色1
    color[v^1] = 2; //相邻的染色2
    S[top++] = v;
    for(int i=first[v];i!=-1;i=e[i].next){
        if(!dfs(e[i].to))return 0;
    }
    return 1;
}

int main()
{
    int a,b;
    while(scanf("%d%d",&n,&m)!=EOF){
        init();
        for(int i=0;i<m;i++){
            scanf("%d%d",&a,&b);
            a--;
            b--;
            addEdge(a,b^1);
            addEdge(b,a^1);
        }
        int k;
        for(int i=0;i<2*n;i+=2){
            if(!color[i]){
                top = 0;
                if(!dfs(i)){
                    while(top){
                        k = S[--top];
                        color[k] = color[k^1] = 0;
                    }
                    if(!dfs(i+1)){  //2*i-1节点不能选择，必然要选择2*i节点，如果还不满足，说明no solution
                        flag = 0;
                        break;
                    }
                }
            }
        }

        if(!flag){
        cout<<"NIE"<<endl;
        continue;
        }
        for(int i=0;i<2*n;i++){
            if(color[i]==1){
                cout<<i+1<<endl;
            }
        }
    }

    //cout << "Hello world!" << endl;
    return 0;
}
/*
6 6
1 3
4 6
5 7
9 11
10 11
5 12
*/