// 解説PDF, https://twitter.com/kyopro_friends/status/1274705953099669505/photo/1
// の通り実装

#include <algorithm>
#include <array>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
#define REP(i,n) for(int i = 0; i < (int)(n); ++i)
#define FOR(i,a,b) for(int i = (a); i < (int)(b); ++i)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(v) ((int)v.size())
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b; return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b; return true;
    }
    return false;
}
template<int MOD> struct Fp {
    ll val;
    constexpr Fp(ll v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator += (const Fp& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        ll a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            ll t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, ll n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
constexpr ll MOD = 1e9 + 7;
using mint = Fp<MOD>;

#define pb push_back
#define mp make_pair
#define mt make_tuple

class NCK {
private:
    ll m_mod;

public:
    // mod must be a prime number
    NCK(ll mod) : m_mod(mod) {}

    // x^y % m_mod
    ll modPow(ll x, ll y)
    {
        ll r = 1, a = x;
        while (y > 0) {
            if ((y&1) == 1) {
                r = (r * a) % m_mod;
            }
            a = (a * a) % m_mod;
            y /= 2;
        }
        return r;
    }

    // a^-1 ≡ a^(p-2) (mod p)   (p is prime)
    ll modInverse(ll x)
    {
        return modPow(x, m_mod-2);
    }

    // Modular division x / y, find modular multiplicative inverse of y
    // and multiply by x.
    ll modDivision(ll p, ll q)
    {
        return (p * modInverse(q)) % m_mod;
    }

    // Binomial coifficient C(n,k) in O(k) time.
    ll choose(ll n, ll k)
    {
        if (k > n) {
            return 0;
        }
        ll p = 1, q = 1;
        for (int i=1; i<=k; i++) {
            q = (q * i) % m_mod;
            p = (p * (n - i + 1)) % m_mod;
        }
        return modDivision(p, q);
    }

    // make nCk table from 0C0 to nCn
    vector<vector<ll>> makeNckTableFrom00ToNN(ll n_max) {
        assert(n_max > 0);
        vector<vector<ll>> table(n_max+1, vector<ll>(n_max+1));
        table[0][0] = 1;
        FOR(i, 1, n_max + 1) {
            table[i][0] = 1;
            FOR(j, 1, n_max + 1) {
                table[i][j] = (table[i - 1][j - 1] + table[i - 1][j]) % m_mod;
            }
        }
        return table;
    }

    // make nCk table from nC0 to nCn
    vector<ll> makeNckTableFromN0ToNN(ll n, ll k_max) {
        assert(n > 0);
        assert(n >= k_max);
        vector<ll> table(n+1);
        table[0] = 1;
        ll p = 1, q = 1;
        table[0] = 1;
        FOR(i, 1, k_max+1) {
            q = (q * i) % m_mod;
            p = (p * (n - i + 1)) % m_mod;
            table[i] = modDivision(p, q);
        }
        return table;
    }

    // make nCk table from n1Ck to n2Ck
    vector<ll> makeTableFromN1CkToN2Ck(ll n1, ll n2, ll k) {
        vector<ll> table;

        // n < kのときは nCk = 0
        FOR(n, n1, k) {
            table.pb(0);
        }

        ll tmp = -1;
        FOR(n, k, n2 + 1) {
            if (n == k) {
                tmp = this->choose(n, k);
            }
            else {
                tmp *= n;
                tmp %= this->m_mod;
                tmp = this->modDivision(tmp, n - k);
            }
            table.pb(tmp);
        }
        return table;
    }

    // make modInverse table from 0 to n_max
    vector<ll> makeModInverseTable(ll n_max) {
        assert(n_max > 0);
        vector<ll> table(n_max + 1);
        FOR(i, 1, n_max + 1) {
            table[i] = modInverse(i);
        }
        return table;
    }
};

mint mypow(ll n, ll k) {
    mint ans = 1;
    REP(i, k) ans *= n;
    return ans;
}

int main(void)
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    ll K; cin >> K;
    string S; cin >> S;

    NCK nck(MOD);
    auto table = nck. makeTableFromN1CkToN2Ck(0, SIZE(S) - 1 + K, SIZE(S) - 1);

    vector<mint> pow26_table;
    mint tmp = 1;
    REP(i, K + 1) {
        pow26_table.pb(tmp);
        tmp *= 26;
    }

    vector<mint> pow25_table;
    tmp = 1;
    REP(i, K + 1) {
        pow25_table.pb(tmp);
        tmp *= 25;
    }

    mint ans = 0;
    REP(i, K + 1) {
        // 追加するK文字のうち、i文字をS[-1]より後ろに、
        // K - i文字をS[-1]より前に配置

        // mint val1 = mypow(26, i);
        mint val1 = pow26_table[i];

        // mint val2 = n_choose_k(SIZE(S) - 1 + (K - i), SIZE(S) - 1);
        mint val2 = table[SIZE(S) - 1 + (K - i)];

        val2 *= pow25_table[K - i];

        // cout << "i, val1, val2 = " << i << "," << val1 << "," << val2 << endl;

        ans += val1 * val2;
    }
    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 43644