import sys
input = sys.stdin.readline

from operator import itemgetter

T,R=map(int,input().split())

A=[]
player=1

for turn in range(T):
    p=list(map(int,input().split()))

    for x in p[1:]:
        A.append((x,player,turn))
        player+=1

    A.sort(key=itemgetter(0))

    ANS=[]

    while len(A)>=4:

        for i in range(len(A)):
            if A[i][2]<turn-10:
                SA=1<<30
                MININD=-1

                for j in range(i-3,i+1):
                    if j>=0 and j+3<len(A):
                        x,y,z,w=A[j][0],A[j+1][0],A[j+2][0],A[j+3][0]
                        k=max(x,y,z,w)-min(x,y,z,w)

                        if k<SA:
                            SA=k
                            MININD=j
                            
                ANS.append((A[MININD][1],A[MININD+1][1]))
                ANS.append((A[MININD+1][1],A[MININD+2][1]))
                ANS.append((A[MININD+2][1],A[MININD+3][1]))

                A=A[:MININD]+A[MININD+4:]
                break

        else:
            break

    if turn==T-1:
        while len(A)>=4:
            ANS.append((A[0][1],A[1][1]))
            ANS.append((A[1][1],A[2][1]))
            ANS.append((A[2][1],A[3][1]))

            A=A[4:]

        if len(A)>=2:
            for i in range(len(A)-1):
                ANS.append(A[i][1],A[i+1][1])

    print(len(ANS),flush=True)
    for x,y in ANS:
        print(x,y,flush=True)