APS_Vezbi_Opseg

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;


public class Range {

    static long proveri(long N, long A, long B) {
        // Vasiot kod tuka

        for (long i = (A+B)/2; A <= B; i = (A+B)/2) {
            long result = (i*i) + s(i) + 200 * i;
            if(result == N) return i;
            else if(result > N) {
                B = i - 1;
            } else {
                A = i + 1;
            }
        }

        return -1;
    }

    static int s(long x) {
        int sum = 0;
        while (x > 0) {
            sum += x%10;
            x /= 10;
        }
        return sum;
    }

    public static void main(String[] args) throws Exception {
        int i,j,k;

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        long N = Long.parseLong(br.readLine());

        StringTokenizer st = new StringTokenizer(br.readLine());
        long A = Long.parseLong(st.nextToken());
        long B = Long.parseLong(st.nextToken());

        long res = proveri(N, A, B);
        System.out.println(res);

        br.close();

    }

}