N,P,K=map(int,input().split())
T=[]
B=[]
for _ in range(N):
    t,b=map(int,input().split())
    T.append(t)
    B.append(b)
ans=0
for i in range(N-K+1):
    tmp=P
    for k in range(K):
        if T[i+k]==1:tmp+=B[i+k]
        else:tmp*=2
    ans=max(ans,tmp)
print(ans if ans<=10**18 else -1)