a,b=map(int,input().split())
n,k=map(int,input().split())

mod=10**9+7

FACT=[1]
for i in range(1,3*10**5+1):
    FACT.append(FACT[-1]*i%mod)

FACT_INV=[pow(FACT[-1],mod-2,mod)]
for i in range(3*10**5,0,-1):
    FACT_INV.append(FACT_INV[-1]*i%mod)

FACT_INV.reverse()

def Combi(a,b):
    if 0<=b<=a:
        return FACT[a]*FACT_INV[b]%mod*FACT_INV[a-b]%mod
    else:
        return 0

print((Combi(n-1,k-1)*a+Combi(n-1,k-2)*b)%mod)

ANS=0
for k in range(1,n+2):
    ANS+=((Combi(n-1,k-1)*a+Combi(n-1,k-2)*b)%mod)**2
    ANS%=mod

print(ANS)