Problem p02632 (C++) — buggy submission, verdict: Runtime Error

//----------BHAVIK DIWANI(PICT_COMP)---------------
#include <bits/stdc++.h>
#define test                                                                   \\
  ll t;                                                                        \\
  cin >> t;                                                                    \\
  while (t--)
#define fastio                                                                 \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define mod 1000000007
#define ll long long
#define int long long
#define endl '\\n'
#define forci(p, q) for (int i = p; i < q; i++)
ll power(ll a, ll b) {
  a %= mod;
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res % mod;
}
ll fact[8999997] = {0};
void facto() {
  fact[0] = 1;
  fact[1] = 1;
  for (int i = 2; i < 8999997; i++)
    fact[i] = (fact[i - 1] * i) % mod;
}
ll ncr(ll n, ll r) {
  ll res = 1;
  res = fact[n];
  res = (res * (power(fact[r], mod - 2))) % mod;
  res = (res * (power(fact[n - r], mod - 2))) % mod;
  return res;
}
using namespace std;
int solve() {
  facto();
  int k;
  cin >> k;
  string s;
  cin >> s;
  int n = s.length();
  int ans = 0;
  for (int i = 0; i <= k; i++) {
    int x = power(26, i);
    int y = power(25, k - i);
    int z = ncr(n + k - i - 1, n - 1);
    int temp = (x * y) % mod;
    temp = (temp * z) % mod;
    ans = (ans + temp) % mod;
  }
  cout << ans;
  return 0;
}
signed main() {
  fastio;
  //	test
  solve();
}

Error: WA

Fixed submission:

//----------BHAVIK DIWANI(PICT_COMP)---------------
#include <bits/stdc++.h>
#include <stdio.h>
#include <stdlib.h>
#define test                                                                   \\
  ll t;                                                                        \\
  cin >> t;                                                                    \\
  while (t--)
#define FOR(p, n) for (ll i = p; i < (ll)n; i++)
#define fastio                                                                 \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define mod 1000000007
#define ll long long
#define int long long
#define ull unsigned long long
#define MAX 1000005
#define pb push_back
#define mkp make_pair
#define vi vector<int>
#define pii pair<int, int>
#define endl '\\n'
#define vs vector<string>
#define mii map<int, int>
#define msi map<string, int>
#define vpii vector<pair<int, int>>
#define vpsi vector<pair<string, int>>
#define forci(p, q) for (int i = p; i < q; i++)
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return (a / gcd(a, b) * b); }
ull power(ull a, ull b) {
  a %= mod;
  ull res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res % mod;
}
ll modmul(ll x, ll y) { return (x * y) % mod; }
ll modadd(ll x, ll y) { return (x + y) % mod; }
ll modsub(ll x, ll y) { return (x - y + mod) % mod; }
ll fact[1000007] = {0};
void facto() {
  fact[0] = 1;
  fact[1] = 1;
  for (int i = 2; i < 1000005; i++)
    fact[i] = (fact[i - 1] * i) % mod;
}
ll ncr(ll n, ll r) {
  ll res = 1;
  res = fact[n];
  res = (res * (power(fact[r], mod - 2))) % mod;
  res = (res * (power(fact[n - r], mod - 2))) % mod;
  return res;
}
ll npr(ll n, ll r) {
  ll res = 1;
  res = fact[n];
  res = (res * (power(fact[n - r], mod - 2))) % mod;
  return res;
}
inline long long toint(const std::string &s) {
  std::stringstream ss;
  ss << s;
  long long x;
  ss >> x;
  return x;
}
inline std::string tostring(long long number) {
  std::stringstream ss;
  ss << number;
  return ss.str();
}
inline std::string tobin(long long x) { return std::bitset<63>(x).to_string(); }
/*bool prime[MAX];
ull sieve(){memset(prime,true,sizeof(prime));for(ull
p=2;p*p<MAX;p++){if(prime[p]==true){for(ull
i=2*p;i<MAX;i+=p){prime[i]=false;}}}prime[0]=0;prime[1]=0;
}*/
/*int inv[1000001]={0};
void findinverse(){inv[1] = 1;for(int i = 2; i <=1e6 ; ++i)	inv[i] = (mod -
(mod/i) * inv[mod%i] % mod) % mod;}
*/
using namespace std;
int solve() {
  facto();
  int k;
  cin >> k;
  string s;
  cin >> s;
  int n = s.length();
  int ans = 0;
  for (int i = 0; i <= k; i++) {
    int x = power(26, i);
    int y = power(25, k - i);
    int z = ncr(n + k - i - 1, n - 1);
    int temp = (x * y) % mod;
    temp = (temp * z) % mod;
    ans = (ans + temp) % mod;
  }
  cout << ans;
  return 0;
}
signed main() {
  fastio;
  //	test
  solve();
}