Buggy python submission (verdict: Runtime Error):
mod = 10**9+7


def inv(a,mod):
    r = [1,0,a]
    w = [0,1,mod]
    while w[2]!=1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0],r[1]-q*w[1],r[2]-q*w[2]]
        r = w
        w = r_new
        x,y = w[0],w[1]    # a*x+y*mod = 1
        return (mod+x%mod)%mod

max_num = 2*10**5+1
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2,max_num):
    fact[i] = fact[i-1] * i % mod

ifact[max_num-1] = inv(fact[max_num-1],mod)

for i in range(2,max_num):
    ifact[max_num-i] = (ifact[max_num-i+1] * (max_num-i+2)) %mod

def comb(x,y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += comb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)


Fixed submission:
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**6+100
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)

Buggy python submission (verdict: Runtime Error):
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**6+1
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)


Fixed submission:
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**6+100
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)

Buggy python submission (verdict: Runtime Error):
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 10**6+1
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)


Fixed submission:
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**6+100
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)

Buggy python submission (verdict: Runtime Error):
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**5+1
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)


Fixed submission:
mod = 10**9+7


def inv(a, mod):
    r = [1, 0, a]
    w = [0, 1, mod]
    while w[2] != 1:
        q = r[2]//w[2]
        r_new = [r[0]-q*w[0], r[1]-q*w[1], r[2]-q*w[2]]
        r = w
        w = r_new
    x, y = w[0], w[1]    # a*x+y*mod = 1
    return (mod+x % mod) % mod


max_num = 2*10**6+100
fact = [0 for _ in range(max_num)]
ifact = [0 for _ in range(max_num)]

fact[0] = fact[1] = 1
ifact[0] = ifact[1] = 1

for i in range(2, max_num):
    fact[i] = fact[i-1] * i % mod
    ifact[i] = ifact[i-1] * inv(i, mod) % mod


def cmb(x, y):
    return fact[x] * ifact[y] * ifact[x-y] % mod


def solve(r, c):
    ans = 0
    for i in range(r+1):
        ans += cmb(c+i+1, c)
        ans %= mod
    return ans


r1, c1, r2, c2 = map(int, input().split())

ans = solve(r2, c2) - solve(r2, c1-1) - solve(r1-1, c2) + solve(r1-1, c1-1)
ans %= mod

print(ans)