import sys
input = sys.stdin.readline

mod = 998244353
H, W, N, K = map(int, input().split())

if H > W:
    H, W = W, H

ans = 0
den = pow((H-K+1)*(W-K+1), mod-2, mod)
if (K-1)*2 <= H:
    ans += (H-2*(K-1))*(W-2*(K-1))*(1-pow(1-K*K*den, N, mod)) % mod
    for i in range(K-1):
        ans += 2*(W-2*(K-1))*(1-pow(1-K*(i+1)*den, N, mod)) % mod
        ans += 2*(H-2*(K-1))*(1-pow(1-K*(i+1)*den, N, mod)) % mod
    for i in range(K-1):
        for j in range(K-1):
            ans += 4*(1-pow(1-(i+1)*(j+1)*den, N, mod)) % mod
elif (K-1)*2 <= W:
    for i in range(H):
        h = max(0, min(i, H-K) - max(0, i-K+1) + 1)
        ans += (W-2*(K-1))*(1-pow(1-h*K*den, N, mod)) % mod
        for j in range(K-1):
            w = max(0, min(j, W-K) - max(0, j-K+1) + 1)
            ans += 2*(1-pow(1-h*w*den, N, mod)) % mod
else:
    for i in range(H):
        for j in range(W):
            h = max(0, min(i, H-K) - max(0, i-K+1) + 1)
            w = max(0, min(j, W-K) - max(0, j-K+1) + 1)
            ans += (1-pow(1-h*w*den, N, mod)) % mod


ans %= mod
print(ans)