N,P,K=map(int,input().split())
inf=1<<60
dp=[-inf]*(K+1)
dp[0]=P
for i in range(N):
    T,B=map(int,input().split())
    for k in range(K,0,-1):
        if T==1:
            x=min(dp[k-1]+B,inf)
        else:
            x=min(dp[k-1]*2,inf)
        dp[k]=max(dp[k],x)
ans=dp[K]
if ans>10**18:
    ans=-1
print(ans)