import std.algorithm, std.array, std.bigint, std.conv, std.stdio, std.typecons, std.range;

void main() {
	auto x = readln[0..$-1];
	auto y = readln[0..$-1];
	if (x.length == y.length) {
		foreach (i; 0 .. y.length) {
			write(x[i], y[i]);
		}
		writeln;
	}
	else if (x.length == y.length+1) {
		foreach (i; 0 .. y.length) {
			write(x[i], y[i]);
		}
		write(x[$-1]);
		writeln;
	}
	else writeln("?");
}