import std.stdio, std.string, std.conv;

void main()
{
	auto ip = readln.split, A = ip[0], B = ip[1], C = ip[2];
	if(A == B){
		writeln(C);
	}
	if(B == C){
		writeln(A);
	}
	if(C == A){
		writeln(B);
	}
}