Buggy python submission (verdict: Runtime Error):
def bit_DP(N.Adj):
    dp=[[0]*N for i in range(1<<N)]
    dp[1][0]=1
    for S in range(1<<N):
        for v in range(N):
            if (S&(1<<v))==0:
                continue
            sub=S^(1<<v)
            
            for u in range(N):
                if (sub&(1<<u)) and (Adj[u][v]):
                    dp[S][v]+=dp[sub][u]
    ans=sum(dp[(1<<N)-1][u] for u in range(1,N))
    return ans
def main():
    N,M=map(int,input().split())
    Adj=[[0]*N for i in range(N)]
    for _ in range(M):
        a,b=map(int,input().split())
        Adj[a-1][b-1]=1
        Adj[b-1][a-1]=1
    ans=bit_dp(N,Adj)
    print(ans)
if __name__=='__main__':
    main()

Fixed submission:
N,M=map(int,input().split())
import copy
a=[0]*M
b=[0]*M
for i in range(M):
    a[i],b[i]=map(int,input().split())
D=[[1]]
def route(D):
    E=[]
    D1=copy.deepcopy(D)
    for j in range(len(D)):
        x=D[j][-1]
        for i in range(M):

            if a[i]==x:
                if not b[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(b[i])
                    E.append(D[j])
            elif b[i]==x:
                if not a[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(a[i])
                    E.append(D[j])
    return E
for i in range(N-1):
    D=copy.deepcopy(route(D))
print(len(D))

Buggy python submission (verdict: Time Limit Exceeded):
N,M=map(int,input().split())
import copy
a=[0]*M
b=[0]*M
for i in range(M):
    a[i],b[i]=map(int,input().split())
D=[[1]]
def route(D):
    E=[]
    D1=copy.deepcopy(D)
    for j in range(len(D)):
        x=D[j][-1]
        for i in range(M):

            if a[i]==x:
                if not b[i] in D1[j]:
                    D=copy.deepcopy(D1)
                    D[j].append(b[i])
                    E.append(D[j])
            elif b[i]==x:
                if not a[i] in D1[j]:
                    D=copy.deepcopy(D1)
                    D[j].append(a[i])
                    E.append(D[j])
    return E
for i in range(N-1):
    D=copy.deepcopy(route(D))
print(len(D))

    

Fixed submission:
N,M=map(int,input().split())
import copy
a=[0]*M
b=[0]*M
for i in range(M):
    a[i],b[i]=map(int,input().split())
D=[[1]]
def route(D):
    E=[]
    D1=copy.deepcopy(D)
    for j in range(len(D)):
        x=D[j][-1]
        for i in range(M):

            if a[i]==x:
                if not b[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(b[i])
                    E.append(D[j])
            elif b[i]==x:
                if not a[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(a[i])
                    E.append(D[j])
    return E
for i in range(N-1):
    D=copy.deepcopy(route(D))
print(len(D))

Buggy python submission (verdict: Runtime Error):
N,M=map(int,input().split())
import copy
a=[0]*M
b=[0]*M
for i in range(M):
    a[i],b[i]=map(int,input().split())
D=[[1]]
def route(D):
    E=[]
    D1=copy.deepcopy(D)
    for j in range(len(D)):
        x=D[j][-1]
        for i in range(M):

            if a[i]==x:
                if not b[i] in D1[j]:
                    D=copy.deepcopy(D1)
                    D[j].append(b[i])
                    E.append(D[j])
            elif b[i]==x:
                if not a[i] in D1[j]:
                    D=copy.deepcopy(D1)
                    D[j].append(a[i])
                    E.append(D[j])
    return E
for i in range(N-1):
    D=copy.deepcopy(route(D))

if len(D[0])!=N:
    print(0)
    exit()
print(len(D))

    

Fixed submission:
N,M=map(int,input().split())
import copy
a=[0]*M
b=[0]*M
for i in range(M):
    a[i],b[i]=map(int,input().split())
D=[[1]]
def route(D):
    E=[]
    D1=copy.deepcopy(D)
    for j in range(len(D)):
        x=D[j][-1]
        for i in range(M):

            if a[i]==x:
                if not b[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(b[i])
                    E.append(D[j])
            elif b[i]==x:
                if not a[i] in D1[j]:
                    D[j]=copy.deepcopy(D1[j])
                    D[j].append(a[i])
                    E.append(D[j])
    return E
for i in range(N-1):
    D=copy.deepcopy(route(D))
print(len(D))