#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

ll N, P, K, T[1010], B[1010];
ll dp[1010][1010];

int main() {
  cin >> N >> P >> K;
  for (int i = 0; i < N; i++) {
    cin >> T[i] >> B[i];
  }
  dp[0][0] = P;
  for (int i = 0; i < K; i++) {
    for (int j = 0; j < N; j++) {
      if (T[j] == 1) dp[i + 1][j + 1] = max(dp[i + 1][j + 1], dp[i][j] + B[j]);
      if (T[j] == 2) dp[i + 1][j + 1] = max(dp[i + 1][j + 1], 2 * dp[i][j]);
      dp[i][j + 1] = max(dp[i][j + 1], dp[i][j]);
    }
  }
  if (dp[K][N] > 1'000'000'000'000'000'000) cout << -1 << endl;
  else cout << dp[K][N] << endl;
  return 0;
}