function Main(input){
	var xs = input.trim().split(' ').map(v=>parseInt(v,10));
    var ans = 0;
    if(xs[1]==xs[2]){
    ans = xs[0];
    }else if(xs[0]==xs[2]){
    ans = xs[1];
    }else if(xs[0]==xs[1]){
    ans = xs[2];
    }
    console.log(ans);  
}
Main(require("fs").readFileSync("/dev/stdin","utf8"));