package main

import . "fmt"
import . "math/big"

func main() {
	var n,k int 
	p:=new(Int)
	Scan(&n,p,&k)
	dp:=make([]*Int,k+1)
	dp[0]=p
	b:=new(Int)
	for ;n>0;n-- {
		var t int
		Scan(&t,b)
		for i:=k-1;i>=0;i-- {
			if dp[i]==nil {
				continue
			}
			x:=new(Int)
			if t==1 {
				x.Add(dp[i],b)
			} else {
				x.Add(dp[i],dp[i])
			}
			if e:=dp[i+1];e==nil||e.Cmp(x)<0 {
				dp[i+1]=x
			}
		}
	}
	if dp[k].Cmp(NewInt(int64(1e18)))>0 {
		Println(-1)
	} else {
		Println(dp[k])
	}
}