#include <bits/stdc++.h>

#define rep(i, n) for(int i = 0; i < n; i++)
using namespace std;

typedef long long ll;

const int INF = 1 << 30;
const ll LLINF = 1LL << 60;

int mod = 1000000007;

int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int A[3]; rep(i, 3) cin >> A[i];
    sort(A, A+3);
    if(A[0] == A[1]) cout << A[2] << endl;
    else if(A[1] == A[2]) cout << A[0] << endl;
    else cout << 0 << endl;
    return 0;
}
//----------BHAVIK DIWANI(PICT_COMP)---------------
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define test ll t; cin>>t; while(t--)
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define mod 1000000007
#define ll long long
#define int long long
#define ull unsigned long long
#define MAX 1000005
#define pb push_back
#define mkp make_pair
#define vi vector<int>
#define pii pair<int,int>
#define endl '\n'
#define vs vector<string>
#define mii map<int,int>
#define msi map<string,int>
#define vpii vector< pair<int, int > >
#define vpsi vector< pair< string ,int > >
#define forci(p,q) for(int i=p;i<q;i++)
ll gcd(ll a,ll b){ if(b==0) return a;    return gcd(b,a%b);}
ll lcm(ll a,ll b) { return (a/gcd(a,b)*b);}
ull power(ull a, ull b) {a %= mod;  ull res = 1;  while (b > 0) { if (b & 1) res = res * a % mod;  a = a * a % mod;  b >>= 1; }  return res%mod; }
ll modmul(ll x, ll y){return (x*y)%mod;}
ll modadd(ll x, ll y){return (x+y)%mod;}
ll modsub(ll x, ll y){return (x-y+mod)%mod;}
ll fact[1000007]={0};
void facto() {fact[0]=1;fact[1]=1;for(int i=2;i<1000007;i++)fact[i]=(fact[i-1]*i)%mod;}
ll ncr(ll n,ll r) {ll res=1; res=fact[n]; res=(res*(power(fact[r],mod-2)))%mod; res=(res*(power(fact[n-r],mod-2)))%mod; return res;}
ll npr(ll n,ll r) {ll res=1; res=fact[n]; res=(res*(power(fact[n-r],mod-2)))%mod; return res;}
inline long long toint(const std::string &s) {std::stringstream ss; ss << s; long long x; ss >> x; return x;}
inline std::string tostring(long long number) {std::stringstream ss; ss << number; return ss.str();}
inline std::string tobin(long long x) {return std::bitset<63>(x).to_string();}
const int inf=1e9;
/*bool prime[MAX];
ull sieve(){memset(prime,true,sizeof(prime));for(ull p=2;p*p<MAX;p++){if(prime[p]==true){for(ull i=2*p;i<MAX;i+=p){prime[i]=false;}}}prime[0]=0;prime[1]=0;
}*/
/*
int inv[1000001]={0};int invf[1000001]={0};
void findinverse(){
	inv[0]=1;
	inv[1] = 1;
	for(int i = 2; i <=1e6 ; ++i)
		inv[i] = (mod - (mod/i) * inv[mod%i] % mod) % mod;
	invf[0]=1;invf[1]=1;
	for(int i=2;i<=1e6;i++){
		invf[i]=invf[i-1]*inv[i]%mod;
	}
}*/
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> orderedSet;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> orderedMultiset;
int solve()
{
	int r1,c1,r2,c2;
	cin>>r1>>c1>>r2>>c2;
	if(r1==r2 && c1==c2){
		cout<<"0"<<endl;
	}
	else if(r1+c1==r2+c2 || r1-c1==r2-c2 || abs(r1-r2)+abs(c1-c2)<=3){
		cout<<"1"<<endl;
	}
	else if((r1+r2+c1+c2)%2==0 || abs(r1-r2)+abs(c1-c2)<=6 || abs((r1-c1)-(r2-c2))<=3 || abs((r1+c1)-(r2+c2))<=3){
		cout<<"2"<<endl;
	}
	else{
			cout<<"3"<<endl;
	}
	return 0;
}
signed main()
{
	fastio;
//	test
		solve();
}



