#include <bits/stdc++.h>

using namespace std;

#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define endl "\n"
#define rep(i, a, b) for (auto i = (a); i < (b); ++i)
#define rrep(i, a, b) for (auto i = (a); i > (b); --i)
#define UNIQUE(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

#ifdef LOCAL_DEFINE
struct InitInput
{
  InitInput()
  {
    FILE *stream1;
    stream1 = freopen("in.txt", "r", stdin);
    assert(stream1 != nullptr);
    cerr << "This problem is not interactive" << endl;
  }
} LOCAL_INPUT;
struct LOCAL_OUTPUT
{
  LOCAL_OUTPUT()
  {
    FILE *stream2;
    const char *outputfile = "out.txt";
    stream2 = freopen(outputfile, "w", stdout);
    assert(stream2 != nullptr);
    cerr << "output [ " << outputfile << " ]" << endl;
  }
} /*LOCAL_OUTPUT*/;
#define show(x) cerr << #x << " = " << (x) << " (line " << __LINE__ << ")" << endl
#define showA(a, n)                                            \
  do                                                           \
  {                                                            \
    for (int _i_t_e_ = 0; _i_t_e_ < (n); _i_t_e_++)            \
      cerr << "(" << _i_t_e_ << " = " << (a)[_i_t_e_] << ") "; \
    cerr << endl;                                              \
  } while (0)
#define showA2(a, n, m)                                                                        \
  do                                                                                           \
  {                                                                                            \
    for (int _i_t_e_ = 0; _i_t_e_ < (n); _i_t_e_++)                                            \
    {                                                                                          \
      for (int _i_t_e_2 = 0; _i_t_e_2 < (m); _i_t_e_2++)                                       \
      {                                                                                        \
        cerr << "(" << _i_t_e_ << ", " << _i_t_e_2 << " = " << (a)[_i_t_e_][_i_t_e_2] << ") "; \
      }                                                                                        \
      cerr << endl;                                                                            \
    }                                                                                          \
    cerr << endl;                                                                              \
  } while (0)
#else
#define show(x)
#define showA(a, n)
#define showA2(a, n, m)
#endif

struct InitAim
{
  InitAim()
  {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.precision(12);
    cout << fixed;
#ifdef LOCAL_DEFINE
    cerr << "This problem is not interactive" << endl;
#endif
  }
} aim_cpo;

typedef long long ll;
typedef unsigned long long ull;

constexpr const int INT_INF = 0x3f3f3f3f;       //1061109567
constexpr const ll LL_INF = 0x3f3f3f3f3f3f3f3f; //4557430888798830399

template <typename T>
bool chmin(T &a, T b) { return a > b ? (a = b, true) : false; }
template <typename T>
bool chmax(T &a, T b) { return a < b ? (a = b, true) : false; }
template <typename T>
void ln(T i, T n) { cout << (i == n - 1 ? "\n" : " "); }
template <typename T, typename S>
ostream &operator<<(ostream &out, const pair<T, S> &pair1)
{
  out << '(' << pair1.fi << ", " << pair1.se << ')';
  return out;
}
template <typename T>
ostream &operator<<(ostream &out, const vector<T> &vector1)
{
  out << '[';
  for (unsigned int i = 0; i < vector1.size(); i++)
  {
    out << vector1[i];
    if (i == vector1.size() - 1)
      out << "]";
    else
      out << ", ";
  }
  return out;
}

// INT
#define GCD(a, b) __gcd(a, b)
template <typename T>
T LCM(T a, T b)
{
  return a / GCD(a, b) * b;
}
template <typename T>
T EXTGCD(T a, T b, T &x, T &y)
{
  T d = a;
  if (b != 0)
  {
    d = EXTGCD(b, a % b, y, x);
    y -= (a / b) * x;
  }
  else
    x = 1, y = 0;
  return d;
}
template <typename T>
bool is_prime(T a)
{
  for (int i = 2; i * i <= a; i++)
    if (a % i == 0)
      return true;
  return false;
}
template <typename T, typename S>
T Pow(T a, S b)
{
  T res = 1, now = a;
  while (b)
  {
    if (b & 1)
      res *= now;
    b >>= 1;
    now *= now;
  }
  return res;
}

// MOD
ll MOD = 1000000000L + 7L;
#define Madd(a, b) (((a) % MOD) + ((b) % MOD)) % MOD
#define Mmul(a, b) (((a) % MOD) * ((b) % MOD)) % MOD
#define Msub(a, b) (((a) % MOD) + MOD - ((b) % MOD)) % MOD
template <typename T, typename S>
T ModPow(T a, S b)
{
  assert(b >= 0);
  T res = 1, now = Msub(a, 0);
  while (b)
  {
    if (b & 1)
      res = Mmul(res, now);
    b >>= 1;
    now = Mmul(now, now);
  }
  return res;
}
template <typename T>
T ModInverse(T a, T mod, bool prime)
{ // if mod is prime, "prime" is true.
  if (prime)
    return ModPow(a, mod - 2);
  else
  {
    T x, y;
    EXTGCD(a, mod, x, y);
    return (mod + x % mod) % mod;
  }
}
template <typename T>
T EulerTotient(T a)
{
  vector<pair<int, int>> v;
  for (T i = 2; i * i <= a; i++)
  {
    int cnt = 0;
    while (a % i == 0)
    {
      cnt++;
      a /= i;
    }
    if (cnt != 0)
      v.emplace_back(i, cnt);
  }
  if (a != 1)
    v.emplace_back(a, 1);
  //showV(v, (int) v.size());
  T res = 1;
  for (int i = 0; i < (int)v.size(); i++)
  {
    if (v[i].se == 1)
    {
      //res *= v[i].fi - 1;
      res = Mmul(res, v[i].fi - 1);
    }
    else
    {
      //res *= Pow(v[i].fi, v[i].se) - Pow(v[i].fi, v[i].se - 1);
      res = Mmul(res, Msub(ModPow(v[i].fi, v[i].se), ModPow(v[i].fi, v[i].se - 1)));
    }
  }
  return res;
}
#define Mdivide(a, b) Mmul(((a) % MOD), (ModInverse((b), MOD, true))) % MOD
ll comb(ll a, ll b)
{
  chmin(b, a - b);
  ll res = 1LL, now = a;
  for (ll i = 1; i <= b; i++)
  {
    res = Mmul(res, now);  //res *= now;
    res = Mdivide(res, i); // res /= i;
    now--;
  }
  return res;
}

///////////////////////////////////////////////////////////////////////////////////
// TEMPLATE(data structure)
///////////////////////////////////////////////////////////////////////////////////

template <typename T>
class BIT
{
public:
  BIT(int size)
  {
    BITTable.assign(++size, 0);
  }
  T sum(int k)
  {
    T res = 0;
    for (++k; k > 0; k -= k & -k)
    {
      res += BITTable[k];
    }
    return res;
  }
  T sum(int l, int r)
  {
    if (l == 0)
      return sum(r);
    return sum(r) - sum(l - 1);
  }
  void update(int k, T x)
  { // b[k] += x;
    for (++k; k < (int)BITTable.size(); k += k & -k)
      BITTable[k] += x;
  }

private:
  vector<T> BITTable;
};

template <typename T>
class IntervalTree
{
  using F = function<T(T, T)>;

public:
  IntervalTree(int n, const F func, const T init) : func(func), init(init)
  {
    size = 1;
    while ((int)size < n)
      size <<= 1;
    table.assign(2 * size, init);
  }
  void set(int k, T &x)
  {
    table[size + k] = x;
  }
  void build()
  {
    for (int i = size - 1; i >= 0; --i)
    {
      table[i] = func(table[i * 2], table[i * 2 + 1]);
    }
  }
  void update(int k, const T &x)
  {
    k += size;
    table[k] = x;
    while (k >>= 1)
    {
      table[k] = func(table[k * 2], table[k * 2 + 1]);
    }
  }
  T query(int a, int b)
  {
    T L = init, R = init;
    for (a += size, b += size; a < b; a >>= 1, b >>= 1)
    {
      if (a & 1)
        L = func(L, table[a++]);
      if (b & 1)
        R = func(table[--b], R);
    }
    return func(L, R);
  }
  T operator[](const int k) const
  {
    return table[k + size];
  }

private:
  unsigned int size;
  vector<T> table;
  const F func;
  const T init;
};

class UnionFind
{
public:
  explicit UnionFind(int _n) : n(_n)
  {
    par.resize(static_cast<unsigned long>(_n));
    rank.resize(static_cast<unsigned long>(_n));
    sizes.resize(static_cast<unsigned long>(_n));
    for (int i = 0; i < _n; i++)
    {
      par[i] = i;
      rank[i] = 0;
      sizes[i] = 1;
    }
  }
  int find(int a)
  {
    if (par[a] == a)
      return a;
    return par[a] = find(par[a]);
  }
  bool same(int a, int b)
  {
    return find(a) == find(b);
  }
  void unite(int a, int b)
  {
    link(find(a), find(b));
  }
  int size(int a)
  {
    return sizes[find(a)];
  }
  void view()
  {
    for (int i = 0; i < n; i++)
    {
      cout << " par"
           << "[" << i << "]=" << par[i] << ((i == n - 1) ? "\n" : ",");
    }
    for (int i = 0; i < n; i++)
    {
      cout << "size"
           << "[" << i << "]=" << sizes[i] << ((i == n - 1) ? "\n" : ",");
    }
    cout << endl;
  }

private:
  void link(int a, int b)
  {
    if (same(a, b))
      return;
    if (rank[a] > rank[b])
    {
      par[b] = a;
      sizes[a] += sizes[b];
      sizes[b] = 0;
    }
    else
    {
      par[a] = b;
      if (rank[a] == rank[b])
        rank[b]++;
      sizes[b] += sizes[a];
      sizes[a] = 0;
    }
  }
  int n;
  vector<int> par;
  vector<int> rank;
  vector<int> sizes;
};

///////////////////////////////////////////////////////////////////////////////////
// MAIN
///////////////////////////////////////////////////////////////////////////////////
// 735134400 約数が1344個ある高度合成数(<= 1e9)
// 897612484786617600 約数が103680個ある高度合成数(<= 1e18)
// 苦手分野 重複順列
// LLの数値をつかう時は最後にLLをつける癖をつけよう

int n, k;
string s;

int main()
{
  cin >> n >> k;
  cin >> s;
  k--;
  s[k] = (char)(s[k] - 'A' + 'a');
  cout << s << endl;
#ifdef LOCAL_DEFINE
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "s." << endl;
  show(MOD);
#endif
  return 0;
}

///////////////////////////////////////////////////////////////////////////////////
// NOTE
///////////////////////////////////////////////////////////////////////////////////


Measured memory_bytes: 256