#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
ll inf=1000000000000000001;
int main()
{
    int n,k;
    ll p;
    cin>>n>>p>>k;
    vector<int> t(n);
    vector<ll> b(n);
    for(int i=0;i<n;i++)cin>>t[i]>>b[i];
    vector<vector<ll>> dp(n+1,vector<ll>(k+1));
    dp[0][0]=p;
    for(int i=0;i<n;i++){
        for(int j=0;j<=k;j++){
            if(j==0)dp[i+1][j]=dp[i][j];
            else{
                
                
                dp[i+1][j]=min(inf,max(dp[i][j],(t[i]==1?dp[i][j-1]+b[i]:dp[i][j-1]*2)));
            }
        }
    }
    if(dp[n][k]==inf)cout<<-1<<endl;
    else cout<<dp[n][k]<<endl;
}