import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

public class N423 {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
	
	void solve()
	{
		int n = ni(), m = ni();
		if(!(1 <= n && n <= 1200))throw new RuntimeException("n");
		if(!(1 <= m && m <= 1200))throw new RuntimeException("m");
		char[] s = ns().toCharArray();
		char[] t = ns().toCharArray();
		if(s.length != n)throw new RuntimeException("s.length != n");
		if(t.length != m)throw new RuntimeException("t.length != m");
		for(char c : s){
			if("ATGC".indexOf(c) == -1)throw new RuntimeException("invalid char in s");
		}
		for(char c : t){
			if("ATGC".indexOf(c) == -1)throw new RuntimeException("invalid char in t");
		}
		
		int[][] dp = new int[n+1][m+1];
		int[][] dprmin = new int[n+1][m+1];
		int[][] dpcmin = new int[n+1][m+1];
		int[][] argdprmin = new int[n+1][m+1];
		int[][] argdpcmin = new int[n+1][m+1];
		int[][][] prev = new int[n+1][m+1][];
		int I = 999999999;
		for(int i = 0;i < n+1;i++){
			for(int j = 0;j < m+1;j++){
				if(i == 0 && j == 0){
					dp[i][j] = 0; continue;
				}
				dp[i][j] = I;
				// replace
				if(i-1 >= 0 && j-1 >= 0){
					int cost = dp[i-1][j-1] + (s[n-1-(i-1)] == t[m-1-(j-1)] ? 0 : 5);
					if(cost < dp[i][j]){
						dp[i][j] = cost;
						prev[i][j] = new int[]{'r', i-1, j-1};
					}
				}
				// add
				if(j-1 >= 0){
					int cost = dpcmin[i][j-1] + 7 + 2*j;
					if(cost < dp[i][j]){
						dp[i][j] = cost;
						prev[i][j] = new int[]{'a', i, argdpcmin[i][j-1]};
					}
				}
				// del
				if(i-1 >= 0){
					int cost = dprmin[i-1][j] + 7 + 2*i;
					if(cost < dp[i][j]){
						dp[i][j] = cost;
						prev[i][j] = new int[]{'d', argdprmin[i-1][j], j};
					}
				}
				if(j == 0 || dp[i][j]-2*j < dpcmin[i][j-1]){
					dpcmin[i][j] = dp[i][j]-2*j;
					argdpcmin[i][j] = j;
				}else{
					dpcmin[i][j] = dpcmin[i][j-1];
					argdpcmin[i][j] = argdpcmin[i][j-1];
				}
				if(i == 0 || dp[i][j]-2*i < dprmin[i-1][j]){
					dprmin[i][j] = dp[i][j]-2*i;
					argdprmin[i][j] = i;
				}else{
					dprmin[i][j] = dprmin[i-1][j];
					argdprmin[i][j] = argdprmin[i-1][j];
				}
			}
		}
		
		out.println(dp[n][m]);
		int r = n, c = m;
		char[] route = new char[n+m+1];
		int p = 0;
		while(true){
			int[] pr = prev[r][c];
			if(pr == null)break;
			if(pr[0] == 'r'){
				route[p++] = 'r';
			}else if(pr[0] == 'a'){
				for(int i = 0;i < c-pr[2];i++){
					route[p++] = 'a';
				}
			}else{
				for(int i = 0;i < r-pr[1];i++){
					route[p++] = 'd';
				}
			}
			r = pr[1]; c = pr[2];
		}
		int sp = 0;
		for(int i = 0;i < p;i++){
			if(route[i] == 'r' || route[i] == 'd'){
				out.print(s[sp++]);
			}else{
				out.print('-');
			}
		}
		out.println();
		int tp = 0;
		for(int i = 0;i < p;i++){
			if(route[i] == 'r' || route[i] == 'a'){
				out.print(t[tp++]);
			}else{
				out.print('-');
			}
		}
		out.println();
	}
	
	public static char[] rev(char[] a)
	{
		for(int i = 0, j = a.length-1;i < j;i++,j--){
			char c = a[i]; a[i] = a[j]; a[j] = c;
		}
		return a;
	}
	
	void run() throws Exception
	{
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//		Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){
//			@Override
//			public void run() {
//				long s = System.currentTimeMillis();
//				solve();
//				out.flush();
//				if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//			}
//		};
//		t.start();
//		t.join();
	}
	
	public static void main(String[] args) throws Exception { new N423().run(); }
	
	private byte[] inbuf = new byte[1024];
	private int lenbuf = 0, ptrbuf = 0;
	
	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }
	
	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private long[] nal(int n)
	{
		long[] a = new long[n];
		for(int i = 0;i < n;i++)a[i] = nl();
		return a;
	}
	
	private char[][] nm(int n, int m) {
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private int[][] nmi(int n, int m) {
		int[][] map = new int[n][];
		for(int i = 0;i < n;i++)map[i] = na(m);
		return map;
	}
	
	private int ni() { return (int)nl(); }
	
	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}