#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  constexpr ll M = 1000000000000000000LL;
  int n, k; ll p; cin >> n >> p >> k;
  vector<ll> dp(k + 1, 0);
  dp[0] = p;
  while (n--) {
    int t, b; cin >> t >> b;
    if (t == 1) {
      for (int j = k - 1; j >= 0; --j) {
        if (dp[j] == 0) continue;
        if (dp[j] + b > M) {
          cout << "-1\n";
          return 0;
        }
        chmax(dp[j + 1], dp[j] + b);
      }
    } else if (t == 2) {
      for (int j = k - 1; j >= 0; --j) {
        if (dp[j] == 0) continue;
        if (dp[j] * 2 > M) {
          cout << "-1\n";
          return 0;
        }
        chmax(dp[j + 1], dp[j] * 2);
      }
    }
  }
  cout << dp[k] << '\n';
  return 0;
}