N = 5*10**4
n, m = 7, 7
x0, y0 = 3, 3
max_steps = 100
v = 1
from collections import defaultdict
from random import randint
dirs = [(1, 0), (-1, 0), (0, 1), (0, -1)]
hsh = defaultdict(int)
for _ in range(N):
    x, y = x0, y0
    step = 0
    found = False
    while step < max_steps:
        r = randint(0, 3)
        dx, dy = dirs[r]
        x += v * dx
        y += v * dy
        step += 1
        if x <= 0 or x >= n - 1 or y <= 0 or y >= m - 1:
            hsh[step] += 1
            found = True
            break
    if not found:
        hsh[0] += max_steps
exp = sum( k * v for k, v in hsh.items()) / sum(hsh.values())

print(exp)