using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    static long[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, p, k) = (c[0], c[1], c[2]);
        var map = NArr(n);
        var dp = new long[k + 1];
        dp[0] = p;
        for (var i = 0; i < n; ++i)
        {
            var ndp = (long[]) dp.Clone();
            for (var j = 0; j + 1 < dp.Length; ++j)
            {
                ndp[j + 1] = Math.Max(ndp[j + 1], map[i][0] == 1 ? (dp[j] + map[i][1]) : (dp[j] * 2));
            }
            if (ndp.Max() > 1_000_000_000_000_000_000)
            {
                WriteLine(-1);
                return;
            }
            dp = ndp;
        }
        WriteLine(dp[^1]);
    }
}