// 2693
#include <bits/stdc++.h>
using namespace std;

int main() {  cin.tie(0)->sync_with_stdio(0);
  const long INF = 1L << 62;
  const long MX = (long)1e18 + 1;
  int N, K;
  long P;
  cin >> N >> P >> K;
  vector<int> T(N+1), B(N+1);
  for (int i = 1; i <= N; i++) {
    cin >> T[i] >> B[i];
  }

  // dp[i][j]: i番目まででj個装備した時の攻撃力の最大値
  vector<vector<long>> dp(N+1, vector<long>(K+1, -1));
  dp[0][0] = P;
  for (int i = 1; i <= N; i++) {
    dp[i] = dp[i-1];
    for (int j = 1; j <= K; j++) {
      if (T[i] == 1) {
        dp[i][j] = max(dp[i][j], dp[i-1][j-1] + B[i]);
      } else {
        dp[i][j] = max(dp[i][j], dp[i-1][j-1] * 2);
      }
      dp[i][j] = min(dp[i][j], MX);
    }
  }
  long ans = dp[N][K];
  if (ans >= MX) ans = -1;
  cout << ans << endl;
  return 0;
}