#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ll N, P, K, T, B, inf=1e18;
    inf += 1;
    cin >> N >> P >> K;
    vector dp(N+1, vector<ll>(K+1));
    dp[0][0] = P;

    for (int i=1; i<=N; i++){
        cin >> T >> B;
        for (int j=0; j<=K; j++){
            dp[i][j] = min(inf, max(dp[i][j], dp[i-1][j]));
            if (T == 1){
                if (j>=1) dp[i][j] = min(inf, max(dp[i][j], dp[i-1][j-1]+B));
            }
            else{
                if (j>=1) dp[i][j] = min(inf, max(dp[i][j], dp[i-1][j-1]*2));
            }
        }
    }

    if (dp[N][K] == inf) cout << -1 << endl;
    else cout << dp[N][K] << endl;

    return 0;
}