from collections import deque


class MF_graph(object):
    def __init__(self, n):
        self.n = n
        self.g = [[] for _ in range(n)]  # to, rev, cap
        self.pos = []

    def add_edge(self, frm, to, cap):
        m = len(self.pos)
        self.pos.append((frm, len(self.g[frm])))
        self.g[frm].append([to, len(self.g[to]), cap])
        self.g[to].append([frm, len(self.g[frm]) - 1, 0])
        return m

    def get_edge(self, i):
        e_to, e_rev, e_cap = self.g[self.pos[i][0]][self.pos[i][1]]
        re_to, _, re_cap = self.g[e_to][e_rev]
        # from, to, cap, flow
        return (re_to, e_to, e_cap + re_cap, re_cap)

    def edges(self):
        m = len(self.pos)
        for i in range(m):
            yield self.get_edge(i)

    def change_edge(self, i, new_cap, new_flow):
        f, s = self.pos[i]
        rf, rs, _ = self.g[f][s]
        self.g[f][s][2] = new_cap - new_flow
        self.g[rf][rs][2] = new_flow
        return

    def dfs(self, s, v, up):
        if v == s:
            return up
        res = 0
        level_v = self.level[v]
        for i in range(self.iter[v], len(self.g[v])):
            u_to, u_rev, _ = self.g[v][i]
            if level_v <= self.level[u_to] or self.g[u_to][u_rev][2] == 0:
                continue
            d = self.dfs(s, u_to, min(up - res, self.g[u_to][u_rev][2]))
            if d <= 0:
                continue
            self.g[v][i][2] += d
            self.g[u_to][u_rev][2] -= d
            res += d
            if res == up:
                break
        return res

    def flow(self, s, t, flow_limit=10**18):
        self.iter = [0] * self.n

        flow = 0
        while flow < flow_limit:
            self.level = [-1] * self.n
            self.level[s] = 0
            que = deque([s])
            while que:
                v = que.popleft()
                for u_to, _, u_cap in self.g[v]:
                    if u_cap == 0 or self.level[u_to] >= 0:
                        continue
                    self.level[u_to] = self.level[v] + 1
                    if u_to == t:
                        break
                    que.append(u_to)

            if self.level[t] == -1:
                break
            self.iter = [0] * self.n
            while flow < flow_limit:
                f = self.dfs(s, t, flow_limit - flow)
                if not f:
                    break
                flow += f
        return flow

    def min_cut(self, s):
        visited = [False] * self.n
        que = deque([s])
        while que:
            v = que.popleft()
            visited[v] = True
            for u_to, _, u_cap in self.g[v]:
                if u_cap and (not visited[u_to]):
                    visited[u_to] = True
                    que.append(u_to)
        return visited


if __name__ == "__main__":
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10 ** 7)

    N, M = map(int, input().split())
    grid = [list(input().rstrip()) for _ in range(N)]

    g = MF_graph(N * M + 2)
    source = N * M
    sink = N * M + 1

    for i in range(N):
        for j in range(M):
            if grid[i][j] == "#":
                continue
            v = i * M + j
            if (i + j) % 2 == 0:
                g.add_edge(source, v, 1)
            else:
                g.add_edge(v, sink, 1)

    for i in range(N):
        for j in range(M):
            if (i + j) % 2 or grid[i][j] == "#":
                continue
            v0 = i * M + j
            if i and grid[i - 1][j] == ".":
                v1 = (i - 1) * M + j
                g.add_edge(v0, v1, 1)
            if j and grid[i][j - 1] == ".":
                v1 = i * M + j - 1
                g.add_edge(v0, v1, 1)
            if i + 1 < N and grid[i + 1][j] == ".":
                v1 = (i + 1) * M + j
                g.add_edge(v0, v1, 1)
            if j + 1 < M and grid[i][j + 1] == ".":
                v1 = i * M + j + 1
                g.add_edge(v0, v1, 1)

    res = g.flow(source, sink)

    for frm, to, cap, flow in g.edges():
        if frm == source or to == sink or flow == 0:
            continue
        i0, j0 = divmod(frm, M)
        i1, j1 = divmod(to, M)
        if i0 == i1 + 1:
            grid[i1][j1] = "v"
            grid[i0][j0] = "^"
        elif j0 == j1 + 1:
            grid[i1][j1] = ">"
            grid[i0][j0] = "<"
        elif i0 == i1 - 1:
            grid[i1][j1] = "^"
            grid[i0][j0] = "v"
        else:
            grid[i1][j1] = "<"
            grid[i0][j0] = ">"

    print(res)
    for g in grid:
        print("".join(g))

Measured memory_bytes: 20240