#include <iostream>
using namespace std;


int main() {
    long long n, a, b;
    cin >> n >> a >> b;
    long long S = a;
    long long E = b;
    while(S <= E) {
        long long middle = (S + E) / 2;
        long long x = (middle * middle) + (200 * middle);
        long long tmp = middle;
        long long zbir = 0;
        while(tmp > 0) {
            zbir += (tmp % 10);
            tmp /= 10;
        }
        x += zbir;

        if(x == n) {
            cout << middle << endl;
            return 0;
        }
        if(x > n) {
            E = middle - 1;
        }
        else {
            S = middle + 1;
        }
    }

    cout << -1 << endl;
    return 0;
}