#include <iostream>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <cstdlib>
#include <map>
#include <set>
#include <queue>
#include <vector>
#include "testlib.h"
using namespace std;

int main() {
	registerValidation();
	string abc = inf.readToken("[0-9]{3,3}", "abc");
	inf.readEoln();
	inf.readEof();
	int c = abc[2] - '0';
	int b = abc[1] - '0';
	int a = abc[0] - '0';
	if (a == b) cout << -1 << endl;
	if (b == c) cout << -1 << endl;
	if (c == a) cout << -1 << endl;
	cout << max(a, max(b, c)) - min(a, min(b, c)) << endl;
}