#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5+10 , OO = 0x3f3f3f3f;

#define clr(arr,val) memset(arr , val , sizeof (arr))
#define loop(i,n) for(int i = 0;i < int(n);i++)
#define rloop(i,n) for(int i = int(n)-1;i >= 0;i--)
#define range(i,a,b) for(int i = int(a);i <= int(b);i++)
#define ALL(v) ((v).begin()) , ((v).end())
#define SZ(v)  ((int)((v).size()))
typedef pair <int,int> pii ;
typedef vector < pii > vii ;
typedef vector < int > vi;
int dx[]={1,0,-1,0};int dy[]={0,1,0,-1}; //4 Direction
//int dx[]={1,1,0,-1,-1,-1,0,1};int dy[]={0,1,1,1,0,-1,-1,-1};//8 direction
//int dx[]={2,1,-1,-2,-2,-1,1,2};int dy[]={1,2,2,1,-1,-2,-2,-1};//Knight Direction
//int dx[6]={2,1,-1,-2,-1,1};int dy[6]={0,1,1,0,-1,-1}; //Hexagonal Direction
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

int n , k;
string s;

int main()
{   

      ios_base::sync_with_stdio(0);
      cin.tie(0);cout.tie(0);



      cin >> n >> k;
      cin >> s;
      s[k] = tolower(s[k]);
      cout << s << "\n";


      return 0;
}