import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Deque;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import java.util.stream.Collectors;

public class Main {

	public static void main(String[] args) throws IOException {
		new Main().solve();
	}

	private void solve() throws IOException {
		try {
			solveA();
			//			solveB();
			//			solveC();
			//			solveD();
			//			solveD2();
			//			 solveE();
			//			 solveF();
		} finally {
			if (in != null) {
				in.close();
			}
			if (out != null) {
				out.flush();
				out.close();
			}
		}

	}

	private void solveA() {
		int n = nextInt();
		int k = nextInt() - 1;
		StringBuilder builder = new StringBuilder(next());

		out.println(builder.replace(k, k + 1, builder.substring(k, k + 1).toLowerCase()).toString());
	}

	private void solveA2() {
		int n = nextInt();
		int k = nextInt();
		String[] wk = next().split("");
		wk[k - 1] = wk[k - 1].toLowerCase();

		String res = Arrays.stream(wk).collect(Collectors.joining(""));

		out.println(res);
	}

	private void solveB() {
		int wk = nextInt();

		int front = wk / 100;
		int back = wk % 100;

		if ((0 < front && front <= 12) && (back <= 0 || back > 12)) {
			out.println("MMYY");
		} else if ((0 < back && back <= 12) && (front <= 0 || front > 12)) {
			out.println("YYMM");
		} else if ((0 < front && front <= 12) && (0 < back && back <= 12)) {
			out.println("AMBIGUOUS");
		} else {
			out.println("NA");
		}

	}

	private void solveC() {
		int n = nextInt();
		int k = nextInt();

		BigDecimal res = new BigDecimal("0");
		for (int i = 1; i <= n; i++) {
			int pow = recursiveC(i, k);
			BigDecimal powB = new BigDecimal("0.5").pow(pow);
			res = res.add(powB);
		}

		out.println(res.divide(new BigDecimal(n), 11, RoundingMode.HALF_UP));
	}

	private int recursiveC(int i, int n) {
		if (i >= n) {
			return 0;
		}
		return recursiveC(i * 2, n) + 1;
	}

	private static class Edge {
		private int from;
		private int to;
		private int cost;
	}

	private void solveD() {
		int n = nextInt();

		int[] u = new int[n - 1];
		int[] v = new int[n - 1];
		int[] w = new int[n - 1];

		Map<Integer, List<Edge>> wk = new TreeMap<Integer, List<Edge>>();

		for (int i = 0; i < n - 1; i++) {
			Edge e = null;
			List<Edge> tmp = null;

			u[i] = nextInt() - 1;
			v[i] = nextInt() - 1;
			w[i] = nextInt();
			int cost = w[i] % 2;
			e = new Edge();
			e.from = u[i];
			e.to = v[i];
			e.cost = cost;
			tmp = wk.getOrDefault(e.from, new ArrayList<Edge>());
			tmp.add(e);
			wk.put(e.from, tmp);

			e = new Edge();
			e.from = v[i];
			e.to = u[i];
			e.cost = cost;
			tmp = wk.getOrDefault(e.from, new ArrayList<Edge>());
			tmp.add(e);
			wk.put(e.from, tmp);
		}
		Deque<Edge> ek = new ArrayDeque<Edge>();
		for (List<Edge> edges : wk.values()) {
			if (edges.size() == 1) {
				ek.addLast(edges.get(0));
				break;
			}
		}
		//		ek.addLast(wk.get(0).get(0));
		int[] res = new int[n];
		res[0] = 0;
		while (!ek.isEmpty()) {
			Edge e = ek.removeLast();
			if (e.cost % 2 == 0) {
				res[e.to] = res[e.from];
			} else {
				res[e.to] = 1 - res[e.from];
			}
			List<Edge> edges = wk.get(e.to);
			for (Edge edge : edges) {
				if (e.from == edge.to) {
					continue;
				}
				//				System.out.println("e / " + e.from + " : " + e.to + " : " + e.cost);
				//				System.out.println("edge / " + edge.from + " : " + edge.to + " : " + edge.cost);
				//				if (edge.cost % 2 == 0) {
				//					res[edge.to] = res[edge.from];
				//				} else {
				//					res[edge.to] = 1 - res[edge.from];
				//				}
				ek.addLast(edge);
				//				if (edge.cost % 2 == 0) {
				//					res[edge.to] = res[edge.from];
				//				} else {
				//					res[edge.to] = 1 - res[edge.from];
				//				}
			}
		}

		for (int resN : res) {
			out.println(resN);
		}

	}

	private void solveD2() {
		int n = nextInt();

		int[] u = new int[n - 1];
		int[] v = new int[n - 1];
		int[] w = new int[n - 1];

		Map<Integer, List<Edge>> wk = new TreeMap<Integer, List<Edge>>();
		for (int i = 0; i < n - 1; i++) {
			Edge e = null;
			List<Edge> tmp = null;

			u[i] = nextInt() - 1;
			v[i] = nextInt() - 1;
			w[i] = nextInt();
			e = new Edge();
			e.from = u[i];
			e.to = v[i];
			e.cost = w[i];
			tmp = wk.getOrDefault(e.from, new ArrayList<Edge>());
			tmp.add(e);
			wk.put(e.from, tmp);

			e = new Edge();
			e.from = v[i];
			e.to = u[i];
			e.cost = w[i];
			tmp = wk.getOrDefault(e.from, new ArrayList<Edge>());
			tmp.add(e);
			wk.put(e.from, tmp);
		}
		int[] res = new int[n];
		dfs(0, -1, 0, res, wk);
		for (int resN : res) {
			out.println(resN);
		}

	}

	private void dfs(int v, int p, int c, int[] res, Map<Integer, List<Edge>> wk) {
		res[v] = c;
		for (Edge e : wk.get(v)) {
			if (e.to == p) {
				continue;
			}
			if (e.cost % 2 == 0) {
				dfs(e.to, v, c, res, wk);
			} else {
				dfs(e.to, v, 1 - c, res, wk);
			}
		}
	}
	/*
	 * OOM
	 */
	//	private void solveD() {
	//		int n = nextInt();
	//
	//		int[] u = new int[n - 1];
	//		int[] v = new int[n - 1];
	//		int[] w = new int[n - 1];
	//		long[][] graph = new long[n][n];
	//		for (int i = 0; i < n; i++) {
	//			Arrays.fill(graph[i], Integer.MAX_VALUE / 2);
	//			graph[i][i] = 0;
	//		}
	//		for (int i = 0; i < n - 1; i++) {
	//			u[i] = nextInt() - 1;
	//			v[i] = nextInt() - 1;
	//			w[i] = nextInt();
	//			int cost = w[i] % 2== 0 ? 2 : 1;
	//			graph[u[i]][v[i]] = cost;
	//			graph[v[i]][u[i]] = cost;
	//		}
	//		for (int i = 0; i < n; i++) {
	//			for (int j = 0; j < n; j++) {
	//				for (int k = 0; k < n; k++) {
	//					graph[j][k] = Long.min(graph[j][k], graph[j][i] + graph[i][k]);
	//				}
	//			}
	//		}
	//		for (int i = 0; i < n; i++) {
	//			long color = 0;
	//			if (i == 0) {
	//				color = 0;
	//			} else {
	//				color = graph[0][i] % 2;
	//			}
	//			out.println(color);
	//		}
	//	}

	private void solveE() {
		int n = nextInt();
		int m = nextInt();

		int[] x = new int[m];
		int[] y = new int[m];
		int[] z = new int[m];
		for (int i = 0; i < n - 1; i++) {
			x[i] = nextInt() - 1;
			y[i] = nextInt() - 1;
			z[i] = nextInt();
		}

		out.println("");
	}

	private void solveF() {
		int n = nextInt();

		out.println("");
	}

	private final PrintWriter out = new PrintWriter(System.out);
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}

	private int readByte() {
		if (hasNextByte())
			return buffer[ptr++];
		else
			return -1;
	}

	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	private void skipUnprintable() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr]))
			ptr++;
	}

	public boolean hasNext() {
		skipUnprintable();
		return hasNextByte();
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public String next() {
		if (!hasNext())
			throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}
}

Measured memory_bytes: 20692