C++ :

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cassert>
#include <complex>
#include <ctime>

#define clr(x,a) memset(x,a,sizeof(x))
#define sz(x) (int)x.size()
#define rep(i,n) for(int i=0;i<n;i++)
#define repeat(i, a, b) for(int i=(a);i<=(b);i++)
#define all(v) (v).begin(), (v).end()
#define Unique(store) store.resize(unique(store.begin(),store.end())-store.begin())
#define X first
#define Y second



using namespace std;
int solve(int a,int b,int c,int d) {
    set< pair<int,int> >se;
    se.insert(make_pair(a,b));
    while (a!=b) {
        if (b>a)
            b-=a;
        else a-=b;
        se.insert(make_pair(a,b));
    }
    se.insert(make_pair(a,b));
    while (c!=d) {
        pair<int,int>cur=make_pair(c,d);
        if (se.count(cur)) return c+d;
        if (d>c) d-=c;
        else c-=d;
    }
    pair<int,int>cur=make_pair(c,d);
    if (se.count(cur)) return c+d;
    return -1;
}
int main () {
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int a,b,c,d;
    while (scanf("%d %d %d %d",&a,&b,&c,&d)!=EOF) {
        //assert(a<=1e5&&b<=1e5&&c<=1e5&&d<=1e5);
        //cout<<"go "<<a<<" "<<b<<" "<<c<<" "<<d<<endl;
        printf("%d\n",solve(a,b,c,d));
    }
    return 0;
}