#include <bits/stdc++.h>
using namespace std;
#define all(v) (v).begin(), (v).end()
using ll = long long;
using ld = long double;
using pint = pair<int, int>;
using pll = pair<ll, ll>;

ll MX = 1e18;
ll dp[1010][1010];

int main() {
    ll N, P, K; cin >> N >> P >> K;
    vector<ll> T(N), B(N);
    for (int i = 0; i < N; i++) cin >> T[i] >> B[i];
    dp[0][0] = P;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j <= K; j++) {
            ll nxt = (T[i] == 1 ? dp[i][j] + B[i] : dp[i][j] * 2);
            if (nxt > MX) {
                cout << -1 << endl;
                return 0;
            }
            dp[i+1][j+1] = max(dp[i][j+1], nxt);
            dp[i+1][j] = max(dp[i+1][j], dp[i][j]);
        }
    }
    cout << (dp[N][K] > MX ? -1 : dp[N][K]) << endl;
}