#include<bits/stdc++.h>
using namespace std;
#define fs first
#define sc second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ALL(A) A.begin(),A.end()
#define RALL(A) A.rbegin(),A.rend()
typedef long long LL;
typedef pair<LL,LL> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const LL mod=1000000007;
const LL LINF=1LL<<62;
const int INF=1<<30;
int dx[]={1,0,-1,0,1,-1,1,-1};
int dy[]={0,1,0,-1,1,-1,-1,1};

int gcd(int a,int b){
    return b?gcd(b,a%b):a;
}

int main(){
    int a,b,c,d;cin >> a >> b >> c >> d;
    if(a==c||b==d) puts("0");
    else{
        int ans = abs(a - c) + abs(b - d);
        cout << ans - gcd(abs(a-c),abs(b-d)) << endl;
    }
    return 0;
}
