#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const ll MX = 1'000'000'000'000'000'001;
void solve() {
  ll n, p, k;
  cin >> n >> p >> k;
  vector<ll> dp(k + 1, -1);
  dp[0] = p;
  rep(ni, n) {
    ll t, b;
    cin >> t >> b;
    for (ll ki = k - 1; ki >= 0; ki--) {
      if (dp[ki] == -1)
        continue;
      dp[ki + 1] = max(dp[ki + 1], dp[ki] * t + b);
      dp[ki + 1] = min(dp[ki + 1], MX);
    }
  }
  ll ans = dp[k];
  if (ans == MX)
    ans = -1;
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}