def dfs( nod ):
    vizitat[nod] = True
    for i in v[nod]:
        if vizitat[i] == False:
            dfs( i )
    stack.append(nod)


def ctc_dfs(nod):
    ctc[nod] = co
    for i in v2[nod]:
        if ctc[i] == 0:
            ctc_dfs( i )


try:
    import sys

    sys.setrecursionlimit(10000)
    fin = open( "ctc.in" )
    s = fin.readline().split()
    n = int( s[0] )
    v = [ [] for i in range (0, n) ]
    v2 = [ [] for i in range (0, n) ]
    for i in fin:
        s = [ int(x)-1 for x in i.split() ]
        v[ s[0] ].append( s[1] )
        v2[ s[1] ].append( s[0] )
    fin.close()

    vizitat = [False] * n
    stack = []
    for i in range( 0, n ):
        if vizitat[i] == False:
            dfs( i )

    co = 0
    ctc = [0] * n
    for i in range( n-1, -1, -1 ):
        if ctc[ stack[i] ] == 0:
            co += 1
            ctc_dfs( stack[i] )

    fout = open( "ctc.out", "w" )
    fout.write( str( co ) + '\n' )
    afisare = [ [] for i in range( 0, n+1 ) ]
    for i in range( 0, n ):
        afisare[ ctc[i] ].append( i+1 )
    for i in range( 1, n + 1 ):
        for j in afisare[i]:
            fout.write( str(j) + " " )
        fout.write( '\n' )
    fout.close()
except RecursionError as re:
    print( re )