import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

int readint() {
    return readln.chomp.to!int;
}

int[] readints() {
    return readln.split.map!(to!int).array;
}

void main() {
    auto xs = readints;
    int[int] m;
    foreach (x; xs)
        m[x]++;

    foreach (k, v; m) {
        if (v == 1)
            writeln(k);
    }
}
