Problem p02632 (python)

Fixed submission:
K=int(input())
S=input()
M=len(S)
N=K+M
mod=10**9+7
ans=pow(26,N,mod)
class Data():
    def __init__(self):
        self.power=1
        self.rev=1     
class Combi():
    def __init__(self,N,mod):
        self.lists=[Data() for _ in range(N+1)]
        self.mod=mod  
        for i in range(2,N+1):
            self.lists[i].power=((self.lists[i-1].power)*i)%self.mod
        self.lists[N].rev=pow(self.lists[N].power,self.mod-2,self.mod)
        for j in range(N,0,-1):
            self.lists[j-1].rev=((self.lists[j].rev)*j)%self.mod

    def combi(self,K,R):
        if K<R:
            return 0
        else:
            return ((self.lists[K].power)*(self.lists[K-R].rev)*(self.lists[R].rev))%self.mod
        
c=Combi(2*10**6,mod)
for i in range(M):
    ans-=c.combi(N,i)*pow(25,N-i,mod)
    ans%=mod
print(ans%mod)

Buggy submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10**7)
input=sys.stdin.readline
K=int(input())
S=input()
M=len(S)
N=K+M
mod=10**9+7
ans=pow(26,N,mod)
class Data():
    def __init__(self):
        self.power=1
        self.rev=1     
class Combi():
    def __init__(self,N,mod):
        self.lists=[Data() for _ in range(N+1)]
        self.mod=mod  
        for i in range(2,N+1):
            self.lists[i].power=((self.lists[i-1].power)*i)%self.mod
        self.lists[N].rev=pow(self.lists[N].power,self.mod-2,self.mod)
        for j in range(N,0,-1):
            self.lists[j-1].rev=((self.lists[j].rev)*j)%self.mod

    def combi(self,K,R):
        if K<R:
            return 0
        else:
            return ((self.lists[K].power)*(self.lists[K-R].rev)*(self.lists[R].rev))%self.mod
        
c=Combi(2*10**6,mod)
for i in range(M):
    ans-=c.combi(N,i)*pow(25,N-i,mod)
    ans%=mod
print(ans)

Buggy submission (verdict: Runtime Error):
import sys
input=sys.stdin.readline
K=int(input())
S=input()
M=len(S)
N=K+M
mod=10**9+7
ans=pow(26,N,mod)
class Data():
    def __init__(self):
        self.power=1
        self.rev=1     
class Combi():
    def __init__(self,N,mod):
        self.lists=[Data() for _ in range(N+1)]
        self.mod=mod  
        for i in range(2,N+1):
            self.lists[i].power=((self.lists[i-1].power)*i)%self.mod
        self.lists[N].rev=pow(self.lists[N].power,self.mod-2,self.mod)
        for j in range(N,0,-1):
            self.lists[j-1].rev=((self.lists[j].rev)*j)%self.mod

    def combi(self,K,R):
        if K<R:
            return 0
        else:
            return ((self.lists[K].power)*(self.lists[K-R].rev)*(self.lists[R].rev))%self.mod
        
c=Combi(2*10**6,mod)
for i in range(M):
    ans-=c.combi(N,i)*pow(25,N-i,mod)
    ans%=mod
print(ans)

Buggy submission (verdict: Runtime Error):
import sys
input=sys.stdin.readline
K=int(input())
S=input()
M=len(S)
N=K+M
mod=10**9+7
ans=pow(26,N,mod)
class Data():
    def __init__(self):
        self.power=1
        self.rev=1     
class Combi():
    def __init__(self,N,mod):
        self.lists=[Data() for _ in range(N+1)]
        self.mod=mod  
        for i in range(2,N+1):
            self.lists[i].power=((self.lists[i-1].power)*i)%self.mod
        self.lists[N].rev=pow(self.lists[N].power,self.mod-2,self.mod)
        for j in range(N,0,-1):
            self.lists[j-1].rev=((self.lists[j].rev)*j)%self.mod

    def combi(self,K,R):
        if K<R:
            return 0
        else:
            return ((self.lists[K].power)*(self.lists[K-R].rev)*(self.lists[R].rev))%self.mod
        
c=Combi(2*10**6,mod)
for i in range(M):
    ans-=c.combi(N,i)*pow(25,N-i,mod)
    ans%=mod
print(ans)