from collections import defaultdict
import sys
import time

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        group_members = defaultdict(list)
        for member in range(self.n):
            group_members[self.find(member)].append(member)
        return group_members

    def __str__(self):
        return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())


stime=time.perf_counter()

T,R=map(int,input().split())
t=0
N=5400
uf=UnionFind(N+1)
p=[-1]*(N+1)
tick=[-1]*(N+1)
room4set=set()

s=set()
# スキル値, プレイヤーi, 出現チック
s.add((-10000000,-1,-1))
s.add((100000000,-1,-1))
pi=1
t_ans=set()

import bisect
while t<3600 :
    nowtime=time.perf_counter()
    L=list(map(int,input().split()))
    # if nowtime - stime >4.85:
    #     t+=1
    #     print(0)
    #     sys.stdout.flush()
    #     continue
    if L[0] == 0:
        t+=1
        continue

    for e in list(s):
        if e == (-10000000,-1,-1) or e ==(100000000,-1,-1):
            continue
        else:
            if t - e[2] >100 or e[1] in room4set:
                s.discard(e)

    for i in range(L[0]):
        # print(s)
        nowi = (L[i+1],pi,t)
        p[pi] = L[i+1]
        tick[pi] = t
        sorteds=sorted(list(s))
        target=bisect.bisect_right(sorteds,nowi)

        used=False
        for _t in list(t_ans):
            if abs(p[pi] - p[_t]) < 3:
                sz=len(uf.members(_t))
                if sz < 4:
                    uf.union(_t, pi)
                    t_ans.add(pi)
                    used = True
                    break

        if abs(sorteds[target-1][0] - L[i+1])<3:
            sz1 = len(uf.members(sorteds[target-1][1]))
            sz2 = len(uf.members(pi))
            if sz1 + sz2 <= 4:
                uf.union(pi, sorteds[target-1][1])
                t_ans.add(pi)
                used = True
                # s.discard(sorteds[target-1])

        if abs(sorteds[target][0] - L[i+1])<3:
            sz1 = len(uf.members(sorteds[target][1]))
            sz2 = len(uf.members(pi))
            if sz1 + sz2 <= 4:
                uf.union(pi, sorteds[target][1])
                t_ans.add(pi)
                used = True
                # s.discard(sorteds[target])

        # if used == False:
        #     s.add(nowi)
        s.add(nowi)

        pi+=1
    t+=1

    # print (t_ans)

    ans4print=[]
    ans4print_num=0
    for ans in list(t_ans):
        m=uf.members(ans)
        if len(m)>=4:
            mls=[]
            for i in range(1,4):#len(m)) :
                mls.append([m[0],m[i]])
                t_ans.discard(m[0])
                t_ans.discard(m[i])
                ans4print_num+=1
                room4set.add(m[0])
                room4set.add(m[i])
            ans4print.append(mls)
        else:
            mls=[]
            for i in range (1,len(m)):
                mls.append([m[0],m[i]])
                ans4print_num+=1
            ans4print.append(mls)

            # min_tick=10000000000
            # for i in range (len(m)):
            #     min_tick = min(min_tick, tick[m[i]])
            # if min_tick < t - 100 :
            #     mls = []
            #     for i in range (1,len(m)):
            #         mls.append([m[0],m[i]])
            #         t_ans.discard(m[0])
            #         t_ans.discard(m[i])
            #         ans4print_num+=1
            #     ans4print.append(mls)

    print(ans4print_num)
    sys.stdout.flush()
    for i in range (len(ans4print)):
        for e in ans4print[i]:
            print(*e)
            sys.stdout.flush()