#include <bits/stdc++.h>
#ifdef LOCAL
#include "./debug.cpp"
#else
#define debug(...)
#define print_line
#endif
using namespace std;
using ll = long long;

ll dp[1111][1111];

int main() {
    int N, K;
    ll P;
    cin >> N >> P >> K;

    dp[0][0] = P;
    for (int i = 0; i < N; i++) {
        int T, B;
        cin >> T >> B;
        for (int j = 0; j <= K; j++) {
            ll val = dp[i][j];
            dp[i + 1][j] = max(dp[i + 1][j], val);
            val = T == 1 ? val + B : val * 2;
            val = min(val, (ll)1e18 + 1);
            dp[i + 1][j + 1] = max(dp[i + 1][j + 1], val);
        }
    }

    ll ans = dp[N][K];
    if (ans == (ll)1e18 + 1) {
        ans = -1;
    }
    cout << ans << endl;
}