#include <bits/stdc++.h>
using namespace std;
const long long Inf = 1e15;
int main() {
  long long a, b, c;
  scanf("%lld %lld %lld", &a, &b, &c);
  long long ans = Inf;
  if ((a + b) % 2 == 0) ans = max(a, b);
  if ((a + c) % 2 == 0) ans = min(max(a, c), ans);
  if ((b + c) % 2 == 0) ans = min(max(b, c), ans);
  if (ans == Inf)
    puts("-1");
  else
    printf("%I64d\n", ans);
  return 0;
}
