package olymp;

import net.egork.utils.io.InputReader;
import net.egork.utils.io.OutputWriter;

public class TaskC {
    class Tariff {
        long packageSize;
        long timeForOneByte;
        long price;

        public Tariff(long packageSize, long timeForOneByte, long price) {
            this.packageSize = packageSize;
            this.timeForOneByte = timeForOneByte;
            this.price = price;
        }
    }

    public void solve(int testNumber, InputReader in, OutputWriter out) {
        long fileSize = in.readInt();
        long timeLimit = in.readInt();
        long time0 = in.readInt();

        Tariff t1 = new Tariff(in.readInt(), in.readInt(), in.readInt());
        Tariff t2 = new Tariff(in.readInt(), in.readInt(), in.readInt());

        long bestPrice = Long.MAX_VALUE;
        for (long times1 = 1; times1 <= (long)(1e7); times1++) {
            long bytesCanDownload1 = times1 * t1.packageSize;
            bytesCanDownload1 = Math.min(bytesCanDownload1, fileSize);
            long timeSpent1 = bytesCanDownload1 * t1.timeForOneByte;
            long moneySpent1 = times1 * t1.price;
            long timeRemaining1 = timeLimit - timeSpent1;
            if (timeRemaining1 < 0) {
                break;
            }
            long bytesRemaining1 = Math.max(0, fileSize - bytesCanDownload1);

            long leftTimes2 = 0, rightTimes2 = (long)1e7, ansTimes2 = -1;
            while (leftTimes2 <= rightTimes2) {
                long times2 = (leftTimes2 + rightTimes2) / 2;
                long bytesCanDownload2 = times2 * t2.packageSize;
                bytesCanDownload2 = Math.min(bytesCanDownload2, bytesRemaining1);
                long timeSpent2 = bytesCanDownload2 * t2.timeForOneByte;
                long timeRemaining2 = timeRemaining1 - timeSpent2;
                if (timeRemaining2 < 0) {
                    rightTimes2 = times2 - 1;
                    continue;
                }

            }

            if (bytesCanDownload1 >= bytesRemaining1) {
                // more times1 makes no sense
                break;
            }
        }

        if (bestPrice == Long.MAX_VALUE) {
            out.printLine(-1);
        } else {
            out.printLine(bestPrice);
        }
    }
}