import std.stdio, std.conv, std.string, std.range, std.typecons, std.format;
import std.algorithm.searching, std.algorithm.sorting, std.algorithm.iteration, std.algorithm.mutation;

void main()
{
    string input = readln().strip();
    auto n = input.reduce!"a<b?b:a"();
    dchar[] res;
    res.length = input.length;
    res[] = n;

    writeln(res);
}
