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;
    	long proverka=broj((B-A)/2 +A);
    	//System.out.println("preracunato: " +broj((B-A)/2)+"  A:"+A+"  B:"+B);
    	if(A==B)
    		return -1;
    	if(proverka>N){
    		return proveri(N,A,(B-A)/2 +A);
    	}
    	else if(proverka<N){

    		return proveri(N,(B-A)/2 + A,B);
    	}
    	else return (B-A)/2 + A;

    }
    public static long s(long i,long suma){
    	if(i<1)
    		return suma;
    	else{
    	suma+=i%10;
    	return s(i/10,suma);
    	}

    }

    public static long broj(long A){
    	return A*A+s(A,0)+200*A;
    }

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

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

        long N = (long) 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();

    }

}