import java.util.Arrays;

class Main {
    public static void main(String[] args) throws Exception {
        FastScanner sc = new FastScanner();
        FastPrintStream pw = new FastPrintStream();
        solve(sc, pw);
        sc.close();
        pw.flush();
        pw.close();
    }

    public static void solve(FastScanner sc, FastPrintStream pw) {
        int n = sc.nextInt();
        int m = sc.nextInt();
        var g = new char[n][];
        Arrays.setAll(g, i -> sc.nextChars(m));
        Digraph<CapEdge> dig = new Digraph<>(n * m + 2);
        int s = n * m;
        int t = s + 1;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (g[i][j] == '#') continue;
                if (((i ^ j) & 1) == 0) {
                    dig.addEdge(new CapEdge(s, i * m + j, 1));
                } else {
                    dig.addEdge(new CapEdge(i * m + j, t, 1));
                }
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = i & 1; j < m; j += 2) {
                if (g[i][j] == '#') continue;
                if (j - 1 >= 0 && g[i][j - 1] == '.') {
                    dig.addEdge(new CapEdge(i * m + j, i * m + (j - 1), 1));
                }
                if (j + 1 < m && g[i][j + 1] == '.') {
                    dig.addEdge(new CapEdge(i * m + j, i * m + (j + 1), 1));
                }
                if (i - 1 >= 0 && g[i - 1][j] == '.') {
                    dig.addEdge(new CapEdge(i * m + j, (i - 1) * m + j, 1));
                }
                if (i + 1 < n && g[i + 1][j] == '.') {
                    dig.addEdge(new CapEdge(i * m + j, (i + 1) * m + j, 1));
                }
            }
        }
        MaxFlow mf = new MaxFlow(dig);
        int ans = (int) mf.fordFulkersonMaxFlow(s, t);
        int cnt = 0;
        for (var e : dig.getEdges()) {
            if (mf.getFlow(e) == 0) continue;
            int u = e.from;
            int v = e.to;
            if (u == s || v == t) continue;
            int ui = u / m, uj = u % m;
            int vi = v / m, vj = v % m;
            if (g[ui][uj] != '.' || g[vi][vj] != '.') {
                throw new AssertionError();
            }
            if (ui == vi) {
                if (uj + 1 == vj) {
                    g[ui][uj] = '>';
                    g[vi][vj] = '<';
                } else if (uj == vj + 1) {
                    g[ui][uj] = '<';
                    g[vi][vj] = '>';
                } else {
                    throw new AssertionError();
                }
            } else if (uj == vj) {
                if (ui + 1 == vi) {
                    g[ui][uj] = 'v';
                    g[vi][vj] = '^';
                } else if (ui == vi + 1) {
                    g[ui][uj] = '^';
                    g[vi][vj] = 'v';
                } else {
                    throw new AssertionError();
                }
            } else {
                throw new AssertionError();
            }
            cnt++;
        }
        if (ans != cnt) throw new AssertionError();
        pw.println(ans);
        for (var gi : g) {
            pw.println(gi);
        }
    }
}

class MaxFlow {
    private static final long INF = Long.MAX_VALUE;

    private final Digraph<CapEdge> dig;
    private final int n;
    private final int[] count;
    private final CapEdge[][] g;

    public MaxFlow(Digraph<CapEdge> capDiraph) {
        this.dig = capDiraph;
        this.n = capDiraph.getV();
        this.count = new int[n];
        this.g = new CapEdge[n][];
        buildGraph();
    }

    public long getFlow(CapEdge e) {
        return g[e.to][e.rev].cap;
    }

    public void changeEdge(int u, int i, long newCap, long newFlow) {
        nonNegativeCheck(newCap, "Capacity");
        if (newFlow > newCap) {
            throw new IllegalArgumentException(
                String.format("Flow %d is greater than capacity %d.", newCap, newFlow)
            );
        }
        CapEdge e = dig.getEdge(u, i);
        CapEdge er = g[e.to][e.rev];
        e.cap = newCap - newFlow;
        er.cap = newFlow;
    }

    private void buildGraph() {
        int[] idx = new int[n];
        for (int i = 0; i < n; i++) {
            count[i] = idx[i] = dig.deg(i);
        }
        for (CapEdge e : dig.getEdges()) {
            int j = e.to;
            count[j]++;
        }
        for (int i = 0; i < n; i++) {
            g[i] = new CapEdge[count[i]];
        }
        for (int u = 0; u < n; u++) {
            int k = dig.deg(u);
            for (int i = 0; i < k; i++) {
                CapEdge e = dig.getEdge(u, i);
                int v = e.to;
                e.rev = idx[v]++;
                CapEdge r = new CapEdge(v, u, 0);
                r.rev = i;
                g[u][i] = e;
                g[v][e.rev] = r;
            }
        }
    }

    public long maxFlow(int s, int t) {
        return flow(s, t, INF);
    }

    public long flow(int s, int t, long flowLimit) {
        rangeCheck(s, 0, n);
        rangeCheck(t, 0, n);
        buildGraph();
        long flow = 0;
        int[] level = new int[n];
        int[] que = new int[n];
        int[] iter = new int[n];
        while (true) {
            java.util.Arrays.fill(level, -1);
            dinicBFS(s, t, level, que);
            if (level[t] < 0) return flow;
            java.util.Arrays.fill(iter, 0);
            while (true) {
                long d = dinicDFS(t, s, flowLimit - flow, iter, level);
                if (d <= 0) break;
                flow += d;
            }
        }
    }

    private void dinicBFS(int s, int t, int[] level, int[] que) {
        int hd = 0, tl = 0;
        que[tl++] = s;
        level[s] = 0;
        while (tl > hd) {
            int u = que[hd++];
            for (CapEdge e : g[u]) {
                int v = e.to;
                if (e.cap <= 0 || level[v] >= 0) continue;
                level[v] = level[u] + 1;
                if (v == t) return;
                que[tl++] = v;
            }
        }
    }

    private long dinicDFS(int cur, int s, long f, int[] iter, int[] level) {
        if (cur == s) return f;
        long res = 0;
        while (iter[cur] < count[cur]) {
            CapEdge er = g[cur][iter[cur]++];
            int u = er.to;
            CapEdge e = g[u][er.rev];
            if (level[u] >= level[cur] || e.cap <= 0) continue;
            long d = dinicDFS(u, s, Math.min(f - res, e.cap), iter, level);
            if (d <= 0) continue;
            e.cap -= d;
            er.cap += d;
            res += d;
            if (res == f) break;
        }
        return res;
    }

    public long fordFulkersonMaxFlow(int s, int t) {
        return fordFulkersonFlow(s, t, INF);
    }

    public long fordFulkersonFlow(int s, int t, long flowLimit) {
        rangeCheck(s, 0, n);
        rangeCheck(t, 0, n);
        buildGraph();
        boolean[] used = new boolean[n];
        long flow = 0;
        while (true) {
            java.util.Arrays.fill(used, false);
            long f = fordFulkersonDFS(s, t, flowLimit - flow, used);
            if (f <= 0) return flow;
            flow += f;
        }
    }

    private long fordFulkersonDFS(int cur, int t, long f, boolean[] used) {
        if (cur == t) return f;
        used[cur] = true;
        for (CapEdge e : g[cur]) {
            if (used[e.to] || e.cap <= 0) continue;
            long d = fordFulkersonDFS(e.to, t, Math.min(f, e.cap), used);
            if (d <= 0) continue;
            e.cap -= d;
            g[e.to][e.rev].cap += d;
            return d;
        }
        return 0;
    }

    public boolean[] minCut(int s) {
        rangeCheck(s, 0, n);
        boolean[] reachable = new boolean[n];
        int[] stack = new int[n];
        int ptr = 0;
        stack[ptr++] = s;
        reachable[s] = true;
        while (ptr > 0) {
            int u = stack[--ptr];
            for (CapEdge e : g[u]) {
                int v = e.to;
                if (reachable[v] || e.cap <= 0) continue;
                reachable[v] = true;
                stack[ptr++] = v;
            }
        }
        return reachable;
    }

    private void rangeCheck(int i, int minInlusive, int maxExclusive) {
        if (i < 0 || i >= maxExclusive) {
            throw new IndexOutOfBoundsException(
                String.format("Index %d out of bounds for length %d", i, maxExclusive)
            );
        }
    }

    private void nonNegativeCheck(long cap, java.lang.String attribute) {
        if (cap < 0) {
            throw new IllegalArgumentException(
                String.format("%s %d is negative.", attribute, cap)
            );
        }
    }
}

abstract class AbstractGraph<Edg extends AbstractEdge> {
    final int n;
    final java.util.ArrayList<Edg> edges;
    final java.util.ArrayList<java.util.ArrayList<Edg>> adj;
    public AbstractGraph(int n) {
        this.n = n;
        this.edges = new java.util.ArrayList<>(n);
        this.adj = new java.util.ArrayList<>(n);
        for (int i = 0; i < n; i++) {
            adj.add(new java.util.ArrayList<>());
        }
    }
    public abstract void addEdge(Edg edge);
    public Edg getEdge(int u, int i) {
        return adj.get(u).get(i);
    }
    public java.util.ArrayList<Edg> getEdges(int u) {
        return adj.get(u);
    }
    public java.util.ArrayList<Edg> getEdges() {
        return edges;
    }
    public int deg(int u) {
        return adj.get(u).size();
    }
    public int getV() {
        return n;
    }
    public int getE() {
        return edges.size();
    }
}

class Graph<Edg extends AbstractEdge> extends AbstractGraph<Edg> {
    public Graph(int n) {
        super(n);
    }
    @SuppressWarnings("unchecked")
    @Override
    public void addEdge(Edg edge) {
        Edg rev = (Edg) edge.reverse();
        adj.get(edge.from).add(edge);
        adj.get(edge.to).add(rev);
        edges.add(edge);
    }
}

class Digraph<Edg extends AbstractEdge> extends AbstractGraph<Edg> {
    public Digraph(int n) {
        super(n);
    }
    @Override
    public void addEdge(Edg edge) {
        adj.get(edge.from).add(edge);
        edges.add(edge);
    }
}

abstract class AbstractEdge implements Comparable<AbstractEdge> {
    public final int from, to;
    public final long cost;
    public AbstractEdge(int from, int to, long cost) {
        this.from = from;
        this.to = to;
        this.cost = cost;
    }
    public AbstractEdge(int from, int to) {
        this(from, to, 1l);
    }
    public abstract AbstractEdge reverse();
    public int compareTo(AbstractEdge o) {
        return Long.compare(cost, o.cost);
    }
}

final class SimpleEdge extends AbstractEdge {
    public SimpleEdge(int from, int to, long cost) {
        super(from, to, cost);
    }
    public SimpleEdge(int from, int to) {
        super(from, to);
    }
    @Override
    public SimpleEdge reverse() {
        return new SimpleEdge(to, from, cost);
    }
}

final class CapEdge extends AbstractEdge {
    long cap;
    int rev;
    public CapEdge(int from, int to, long cap, long cost) {
        super(from, to, cost);
        this.cap = cap;
    }
    public CapEdge(int from, int to, long cap) {
        this(from, to, cap, 1);
    }
    @Override
    public AbstractEdge reverse() {
        throw new UnsupportedOperationException();
    }
}

class FastPrintStream implements AutoCloseable {
    private static final int BUF_SIZE = 1 << 15;
    private final byte[] buf = new byte[BUF_SIZE];
    private int ptr = 0;
    private final java.lang.reflect.Field strField;
    private final java.nio.charset.CharsetEncoder encoder;

    private java.io.OutputStream out;

    public FastPrintStream(java.io.OutputStream out) {
        this.out = out;
        java.lang.reflect.Field f;
        try {
            f = java.lang.String.class.getDeclaredField("value");
            f.setAccessible(true);
        } catch (NoSuchFieldException | SecurityException e) {
            f = null;
        }
        this.strField = f;
        this.encoder = java.nio.charset.StandardCharsets.US_ASCII.newEncoder();
    }

    public FastPrintStream(java.io.File file) throws java.io.IOException {
        this(new java.io.FileOutputStream(file));
    }

    public FastPrintStream(java.lang.String filename) throws java.io.IOException {
        this(new java.io.File(filename));
    }

    public FastPrintStream() {
        this(System.out);
        try {
            java.lang.reflect.Field f = java.io.PrintStream.class.getDeclaredField("autoFlush");
            f.setAccessible(true);
            f.set(System.out, false);
        } catch (IllegalAccessException | IllegalArgumentException | NoSuchFieldException e) {
            // ignore
        }
    }

    public FastPrintStream println() {
        if (ptr == BUF_SIZE) internalFlush();
        buf[ptr++] = (byte) '\n';
        return this;
    }

    public FastPrintStream println(java.lang.Object o) {
        return print(o).println();
    }

    public FastPrintStream println(java.lang.String s) {
        return print(s).println();
    }

    public FastPrintStream println(char[] s) {
        return print(s).println();
    }

    public FastPrintStream println(char c) {
        return print(c).println();
    }

    public FastPrintStream println(int x) {
        return print(x).println();
    }

    public FastPrintStream println(long x) {
        return print(x).println();
    }

    public FastPrintStream println(double d, int precision) {
        return print(d, precision).println();
    }

    private FastPrintStream print(byte[] bytes) {
        int n = bytes.length;
        if (ptr + n > BUF_SIZE) {
            internalFlush();
            try {
                out.write(bytes);
            } catch (java.io.IOException e) {
                throw new RuntimeException();
            }
        } else {
            System.arraycopy(bytes, 0, buf, ptr, n);
            ptr += n;
        }
        return this;
    }

    public FastPrintStream print(java.lang.Object o) {
        return print(o.toString());
    }

    public FastPrintStream print(java.lang.String s) {
        if (strField == null) {
            return print(s.getBytes());
        } else {
            try {
                return print((byte[]) strField.get(s));
            } catch (IllegalAccessException e) {
                return print(s.getBytes());
            }
        }
    }

    public FastPrintStream print(char[] s) {
        try {
            return print(encoder.encode(java.nio.CharBuffer.wrap(s)).array());
        } catch (java.nio.charset.CharacterCodingException e) {
            byte[] bytes = new byte[s.length];
            for (int i = 0; i < s.length; i++) {
                bytes[i] = (byte) s[i];
            }
            return print(bytes);
        }
    }

    public FastPrintStream print(char c) {
        if (ptr == BUF_SIZE) internalFlush();
        buf[ptr++] = (byte) c;
        return this;
    }

    public FastPrintStream print(int x) {
        if (x == 0) {
            if (ptr == BUF_SIZE) internalFlush();
            buf[ptr++] = '0';
            return this;
        }
        int d = len(x);
        if (ptr + d > BUF_SIZE) internalFlush();
        if (x < 0) {
            buf[ptr++] = '-';
            x = -x;
            d--;
        }
        int j = ptr += d; 
        while (x > 0) {
            buf[--j] = (byte) ('0' + (x % 10));
            x /= 10;
        }
        return this;
    }

    public FastPrintStream print(long x) {
        if (x == 0) {
            if (ptr == BUF_SIZE) internalFlush();
            buf[ptr++] = '0';
            return this;
        }
        int d = len(x);
        if (ptr + d > BUF_SIZE) internalFlush();
        if (x < 0) {
            buf[ptr++] = '-';
            x = -x;
            d--;
        }
        int j = ptr += d; 
        while (x > 0) {
            buf[--j] = (byte) ('0' + (x % 10));
            x /= 10;
        }
        return this;
    }

    public FastPrintStream print(double d, int precision) {
        if (d < 0) {
            print('-');
            d = -d;
        }
        d += Math.pow(10, -d) / 2;
        print((long) d).print('.');
        d -= (long) d;
        for(int i = 0; i < precision; i++){
            d *= 10;
            print((int) d);
            d -= (int) d;
        }
        return this;
    }

    private void internalFlush() {
        try {
            out.write(buf, 0, ptr);
            ptr = 0;
        } catch (java.io.IOException e) {
            throw new RuntimeException(e);
        }
    }

    public void flush() {
        try {
            out.write(buf, 0, ptr);
            out.flush();
            ptr = 0;
        } catch (java.io.IOException e) {
            throw new RuntimeException(e);
        }
    }

    public void close() {
        try {
            out.close();
        } catch (java.io.IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static int len(int x) {
        int d = 1;
        if (x >= 0) {d = 0; x = -x;}
        int p = -10;
        for (int i = 1; i < 10; i++, p *= 10) if (x > p) return i + d;
        return 10 + d;
    }

    private static int len(long x) {
        int d = 1;
        if (x >= 0) {d = 0; x = -x;}
        long p = -10;
        for (int i = 1; i < 19; i++, p *= 10) if (x > p) return i + d;
        return 19 + d;
    }
}

class FastScanner implements AutoCloseable {
    private final java.io.InputStream in;
    private final byte[] buf = new byte[2048];
    private int ptr = 0;
    private int buflen = 0;

    public FastScanner(java.io.InputStream in) {
        this.in = in;
    }

    public FastScanner() {
        this(System.in);
    }

    private boolean hasNextByte() {
        if (ptr < buflen) return true;
        ptr = 0;
        try {
            buflen = in.read(buf);
        } catch (java.io.IOException e) {
            throw new RuntimeException(e);
        }
        return buflen > 0;
    }

    private int readByte() {
        return hasNextByte() ? buf[ptr++] : -1;
    }

    public boolean hasNext() {
        while (hasNextByte() && !(32 < buf[ptr] && buf[ptr] < 127)) ptr++;
        return hasNextByte();
    }

    private StringBuilder nextSequence() {
        if (!hasNext()) throw new java.util.NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        for (int b = readByte(); 32 < b && b < 127; b = readByte()) {
            sb.appendCodePoint(b);
        }
        return sb;
    }

    public String next() {
        return nextSequence().toString();
    }

    public String next(int len) {
        return new String(nextChars(len));
    }

    public char nextChar() {
        if (!hasNextByte()) throw new java.util.NoSuchElementException();
        return (char) readByte();
    }

    public char[] nextChars() {
        StringBuilder sb = nextSequence();
        int l = sb.length();
        char[] dst = new char[l];
        sb.getChars(0, l, dst, 0);
        return dst;
    }
    public char[] nextChars(int len) {
        if (!hasNext()) throw new java.util.NoSuchElementException();
        char[] s = new char[len];
        int i = 0;
        int b = readByte();
        while (32 < b && b < 127 && i < len) {
            s[i++] = (char) b; b = readByte();
        }
        if (i != len) {
            throw new java.util.NoSuchElementException(
                String.format("Next token has smaller length than expected.", len)
            );
        }
        return s;
    }
    public long nextLong() {
        if (!hasNext()) throw new java.util.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 = n * 10 + b - '0';
            } else if (b == -1 || !(32 < b && b < 127)) {
                return minus ? -n : n;
            } else throw new NumberFormatException();
            b = readByte();
        }
    }
    public int nextInt() {
        return Math.toIntExact(nextLong());
    }
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    public void close() {
        try {
            in.close();
        } catch (java.io.IOException e) {
            throw new RuntimeException(e);
        }
    }
}


Measured memory_bytes: 41988