Buggy python submission (verdict: Runtime Error):
N=int(input())
edge=[[] for i in range(N)]
for i in range(N-1):
    a,b=map(int,input().split())
    edge[a-1].append(b-1)
    edge[b-1].append(a-1)

depth=[0]*N
def dfs(v,pv):
    for nv in edge[v]:
        if nv!=pv:
            depth[nv]=depth[v]+1
            dfs(nv,v)

dfs(0,-1)

even=0
odd=0
for i in range(N):
    if depth[i]%2==0:
        even+=1
    else:
        odd+=1

ans=[0 for i in range(N)]

if N%3==0:
    if min(even,odd)>=N//3:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3>even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
elif N%3==2:
    if min(even,odd)>=N//3+1:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3+1>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3+1>even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
else:
    if even>=N//3+1 and odd>=N//3:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif even>=N//3 and odd>=N//3+1:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==1:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3>=even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)

Fixed submission:
import sys

input=sys.stdin.readline
sys.setrecursionlimit(10**7)

N=int(input())
edge=[[] for i in range(N)]
for i in range(N-1):
    a,b=map(int,input().split())
    edge[a-1].append(b-1)
    edge[b-1].append(a-1)

depth=[0]*N
def dfs(v,pv):
    for nv in edge[v]:
        if nv!=pv:
            depth[nv]=depth[v]+1
            dfs(nv,v)

dfs(0,-1)

even=0
odd=0
for i in range(N):
    if depth[i]%2==0:
        even+=1
    else:
        odd+=1

ans=[0 for i in range(N)]

if N%3==0:
    if min(even,odd)>=N//3:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3>even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
elif N%3==2:
    if min(even,odd)>=N//3+1:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3+1>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3+1>even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
else:
    if even>=N//3+1 and odd>=N//3:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==0:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif even>=N//3 and odd>=N//3+1:
        evencount=0
        oddcount=0
        allcount=0
        for i in range(N):
            if depth[i]%2==1:
                if N//3+1>evencount:
                    ans[i]=evencount*3+1
                    evencount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
            else:
                if N//3>oddcount:
                    ans[i]=oddcount*3+2
                    oddcount+=1
                else:
                    ans[i]=(allcount+1)*3
                    allcount+=1
        print(*ans)
    elif N//3>=even:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==0:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==1:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)
    else:
        allcount=0
        d=1
        for i in range(N):
            if depth[i]%2==1:
                ans[i]=3*allcount+3
                allcount+=1
        for i in range(N):
            if depth[i]%2==0:
                if N//3>allcount:
                    ans[i]=3*allcount+3
                    allcount+=1
                else:
                    ans[i]=d
                    if d%3==1:
                        d+=1
                    else:
                        d+=2
        print(*ans)