#include<bits/stdc++.h>
#include <iostream>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
using ll = long long;
ll N,P,K;
vector<ll> T,B;
using Pll = pair<ll,ll>;

ll next_P(ll P,ll T,ll B){
	if(T == 1) return min(P + B,1000'000'000'000'000'001ll);
	return min(P *2,1000'000'000'000'000'001ll);
}

void solve(){
	vector<vector<ll>> dp(N+1,vector<ll>(K+1,-1));
	dp[0][0] = P;
	for(ll i = 0;i<N;i++){
		for(ll j = 0;j<=K;j++){
			if(dp[i][j] == -1) continue;
			dp[i+1][j] = max(dp[i+1][j],dp[i][j]);
			if(j+1<=K)
			dp[i+1][j+1] = max(dp[i+1][j+1],next_P(dp[i][j],T[i],B[i]));
		}
	}
	ll ans = dp[N][K];
	if(ans>1'000'000'000'000'000'000) ans = -1;
	cout << ans << endl;
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cin >> N >> P >> K;
	T.resize(N);
	B.resize(N);
	for(ll i=0;i<N;i++){
		cin >> T[i] >> B[i];
	}
	solve();
}