import java.util.ArrayList;
import java.util.List;

class Euler40 {

    private static class Options {
        int maxPower = 6;
        boolean runCheckpoints = true;
    }

    private static boolean parseIntAfterPrefix(String arg, String prefix, int[] outValue) {
        if (!arg.startsWith(prefix)) {
            return false;
        }
        String tail = arg.substring(prefix.length());
        if (tail.isEmpty()) {
            return false;
        }

        int parsed = 0;
        for (int i = 0; i < tail.length(); i++) {
            char c = tail.charAt(i);
            if (c < '0' || c > '9') {
                return false;
            }
            parsed = parsed * 10 + (c - '0');
        }
        outValue[0] = parsed;
        return true;
    }

    private static boolean parseArguments(String[] args, Options options) {
        for (String arg : args) {
            if ("--skip-checkpoints".equals(arg)) {
                options.runCheckpoints = false;
                continue;
            }
            int[] value = new int[1];
            if (parseIntAfterPrefix(arg, "--max-power=", value)) {
                options.maxPower = value[0];
                continue;
            }
            System.err.println("Unknown argument: " + arg);
            return false;
        }
        return options.maxPower >= 0;
    }

    private static long solve(int maxPower) {
        List<Integer> targets = new ArrayList<>();
        int t = 1;
        for (int p = 0; p <= maxPower; p++) {
            targets.add(t);
            if (t > Integer.MAX_VALUE / 10) {
                throw new RuntimeException("target overflow");
            }
            t *= 10;
        }

        int maxTarget = targets.get(targets.size() - 1);

        long product = 1;
        int nextTargetIndex = 0;
        int globalPos = 0;

        for (int n = 1; globalPos < maxTarget; n++) {
            String s = String.valueOf(n);
            for (int i = 0; i < s.length(); i++) {
                char c = s.charAt(i);
                globalPos++;
                if (globalPos == targets.get(nextTargetIndex)) {
                    product *= (long)(c - '0');
                    nextTargetIndex++;
                    if (nextTargetIndex >= targets.size()) {
                        return product;
                    }
                }
            }
        }

        return product;
    }

    private static boolean runCheckpoints() {
        if (solve(2) != 5L) {
            System.err.println("Checkpoint failed for max_power=2");
            return false;
        }
        if (solve(0) != 1L) {
            System.err.println("Checkpoint failed for max_power=0");
            return false;
        }
        return true;
    }

    public static void main(String[] args) {
        Options options = new Options();
        if (!parseArguments(args, options)) {
            System.exit(1);
        }
        if (options.runCheckpoints && !runCheckpoints()) {
            System.exit(2);
        }

        try {
            System.out.println(solve(options.maxPower));
        } catch (RuntimeException ex) {
            System.err.println(ex.getMessage());
            System.exit(3);
        }
    }
}