Buggy python submission (verdict: Runtime Error):
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)
val1 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)

val2 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

ans = wa - val1 - val2
for i in range(100):
if ans < 0:
    ans += 10 ** 9 + 7
print(ans)

Fixed submission:
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)
val1 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)

val2 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

ans = wa - val1 - val2
for i in range(100):
    if ans < 0:
        ans += 10 ** 9 + 7
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x *= n-i % (10 ** 9 + 7)
    y *= i+1 % (10 ** 9 + 7)
val1 = x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7) % (10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x *= n-i % (10 ** 9 + 7)
    y *= i+1 % (10 ** 9 + 7)

val2 = x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7) % (10 ** 9 + 7)
print(wa - val1 - val2)

Fixed submission:
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)
val1 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)

val2 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

ans = wa - val1 - val2
for i in range(100):
    if ans < 0:
        ans += 10 ** 9 + 7
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x *= n-i % (10 ** 9 + 7)
    y *= i+1 % (10 ** 9 + 7)
val1 = x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x *= n-i % (10 ** 9 + 7)
    y *= i+1 % (10 ** 9 + 7)

val2 = x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)  
ans = wa - val1 -val2
for i in range(10000):
    if ans < 0:
        ans += 10 ** 9 + 7
    else:
        break
print(ans)

Fixed submission:
n,a,b = map(int,input().split())

#制限なしで全ての花束の作り方
wa = pow(2, n, 10 ** 9 + 7) - 1

#a本の花束の作り方
#val1 = comb(n, a, exact=True)
#val2 = comb(n, b, exact = True)

x = 1
y = 1
for i in range(a):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)
val1 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

x = 1
y = 1
for i in range(b):
    x = (x * (n-i)) % (10 ** 9 + 7)
    y = (y * (i+1)) % (10 ** 9 + 7)

val2 = (x * pow(y, 10 ** 9 + 7 - 2, 10 ** 9 + 7)) % (10 ** 9 + 7)

ans = wa - val1 - val2
for i in range(100):
    if ans < 0:
        ans += 10 ** 9 + 7
print(ans)