Language: C++

#define _CRT_SECURE_NO_WARNINGS
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i,n) for(int i=0;i<(lint)(n);i++)
#define REP(i,n) for(int i=1;i<=(lint)(n);i++)
#define all(V) V.begin(),V.end()
#define stackReplaceBegin(size)\
	void* p=malloc(size);\
	esp_new=(lint)p+size-1;\
	void * stack_extend_memory_ = malloc(size);\
	void * stack_extend_origin_memory_;\
	char * stack_extend_dummy_memory_ = (char*)alloca((1+(int)(((long long)stack_extend_memory_)&127))*16);\
	*stack_extend_dummy_memory_ = 0;\
	asm volatile("mov %%rsp, %%rbx\nmov %%rax, %%rsp":"=b"(stack_extend_origin_memory_):"a"((char*)stack_extend_memory_+(size)-1024));
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<lint, lint> P;
constexpr int INF = INT_MAX/2;
constexpr lint LINF = LLONG_MAX/2;
constexpr double eps = DBL_EPSILON;
constexpr double PI=3.141592653589793238462643383279;
lint esp_new;
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
inline lint gcd(lint a, lint b) {
	while (b) {
		lint c = a;
		a = b; b = c % b;
	}
	return a;
}
inline lint lcm(lint a, lint b) {
	return a / gcd(a, b) * b;
}
bool isprime(lint n) {
	if (n == 1)return false;
	for (int i = 2; i * i <= n; i++) {
		if (n % i == 0)return false;
	}
	return true;
}
template<typename T>
T mypow(T a, unsigned int b) {
	T res(1),now(a);
	while(b){
		if(b&1)res*=now;
		b>>=1;
		now*=now;
	}
	return res;
}
template<typename T>
void printArray(std::vector<T>& vec) {
	rep(i, vec.size() - 1)std::cout << vec[i] << " ";
	std::cout << vec.back() << std::endl;
}
template<typename T>
void printArray(T l, T r) {
	T rprev = r;
	rprev--;
	for (T i = l; i != rprev; i++) {
		std::cout << *i << " ";
	}
	std::cout << *rprev << std::endl;
}
lint modpow(lint a,lint b,int m){
	lint res(1),now(a);
	while(b){
		if(b&1){
			res*=now;
			res%=m;
		}
		b>>=1;
		now*=now;
		now%=m;
	}
	return res;
}
constexpr int mod=1000000007;
int k,n=-1,cnt=13;
char c[15];
lint fact[2000010],inv[2000010];
int main(){
	while(true){
		*c=getchar_unlocked();
		if(*c=='\n')break;
		k*=10;
		k+=*c-'0';
	}
	while(getchar_unlocked()!=-1)n++;
	fact[0]=1;
	for(int i=1;i<=n+k;i++)fact[i]=fact[i-1]*i%mod;
	inv[n+k]=modpow(fact[n+k],mod-2,mod);
	for(int i=n+k-1;i>=0;i--)inv[i]=inv[i+1]*(i+1)%mod;
	lint ans=1;now=1;
	for(int i=1;i<=k;i++){
		now*=25;
		now%=mod;
		ans+=fact[n+k]*inv[n+k-i]%mod*inv[i]%mod*now;
		ans%=mod;
	}
	*(c+14)='\n';
	while(ans){
		*(c+cnt)=ans%10+'0';
		ans/=10;
		cnt--;
	}
	fwrite(c+cnt+1,1,14-cnt,stdout);
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:137:20: error: 'now' was not declared in this scope; did you mean 'pow'?
  137 |         lint ans=1;now=1;
      |                    ^~~
      |                    pow