#include <bits/stdc++.h>
#include <iomanip>
#define rep(i,n) for (int i = (int)(0); i < (int)(n); i++)
#define rep1(i,n) for (int i = (int)(1); i <= (int)(n); i++)
#define REP(i,s,n) for (int i = (int)(s); i < (int)(n); i++)
#define mrep(i,s,n) for (int i = (int)(s) - 1; i >= (int)(n); i--)
#define fore(i,a) for(auto &i:a)
#define all(c) begin(c), end(c)
#define rall(x) x.rbegin(), x.rend()
#define vcsort(x) sort(all(x))
#define rev(x) reverse(all(x))
#define vcerase(x) x.erase(unique(all(x)),x.end())
#define vcsum(x) accumulate(all(x),0)
#define vcmax(x) *max_element(all(x))
#define vcmin(x) *min_element(all(x))
#define FI first
#define SE second
#define pb(x) push_back(x)
#define ppb(x) pop_back(X)
#define EL '\n'
#define v(type, name, ...) vector<type> name(__VA_ARGS__)
#define vv(type, name, h, ...) vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define vvv(type, name, h, w, ...) vector<vector<vector<type>>> name(h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
//#define print(x) cout << x << "\n";
//-----
using namespace std;
using ll = long long;
using Ul = unsigned long long;
using cl = const ll;
using VI = vector<int>;
using VS = vector<string>;
using VC = vector<char>;
using VL = vector<ll>;
using VB = vector<bool>;
using PI = pair<int, int>;
using PL = pair<ll, ll>;
using SI = set<int>;
using MII = map<int, int>;
using MIS = map<int, string>;
using MSI = map<string, int>;
template<class t> using V = vector<t>;
template< typename T >  //vector<int> a(n); cin >> a;
ostream &operator<<(ostream &os, const vector< T > &v) {
    for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != (int) v.size() ? " " : "");
    }
    return os;
}
template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
    for(T &in : v) is >> in;
    return is;
}
//-tekito-
int GCD(int a, int b) {if(b == 0){return a;}return GCD(b,a % b);}//最大公約数
int LCM(int a, int b) {return a/GCD(a, b)*b;}//最小公倍数
ll llsm1(ll n) { return (n * (n + 1)) / 2; }//1~nの総和
int kaijo(int n) {if(n==0||n==1){return 1;}else{return n*kaijo(n - 1);}}//階乗
int ketaSum(int num) {int digit_sum=0;while(num>0){digit_sum+=num%10;num/=10;}return digit_sum;}//各桁の和
string revstr(const string& str) {string reversed=str;reverse(reversed.begin(),reversed.end());return reversed;}//文字列反転
bool isPrime(int n) {if(n<2){return false;}for(int i=2;i*i<=n;i++){if(n%i==0){return false;}}return true;}
int getNthPrime(int n) {std::vector<bool> isPrime(1e7, true);isPrime[0] = isPrime[1] = false;int count = 0;
    int prime = 2;while (count < n) {if (isPrime[prime]) {count++;if (count == n)break;for (int i = prime * 2; i < 1e7; i += prime)isPrime[i] = false;}prime++;}return prime;}
long long ppow(int base, int exponent) {long long result=1;while(exponent>0){if(exponent%2==1){result*=base;}base*=base;exponent/=2;}return result;}
char getAlp(int a) {if(a>0||a<27){return'A'+a-1;}}
char getalp(int a) {if(a>0||a<27){return'a'+a-1;}}
int getAlpin(char a) {if(a>='A'||a<='Z'){return a-64;}}
int getalpin(char a) {if(a>='a'||a<='z'){return a-96;}}
template<class t,class u> bool chmax(t&a,u b) {if(a<b){a=b;return true;}else return false;}
template<class t,class u> bool chmin(t&a,u b) {if(b<a){a=b;return true;}else return false;}
//-io-
void fix(int a){cout << fixed << setprecision(a);}
void ent() { cout << "\n";}//print()
void OYN(bool a){cout << (a ? "YES" : "NO") << "\n";}
void Oyn(bool a){cout << (a ? "Yes" : "No") << "\n";}
void oyn(bool a){cout << (a ? "yes" : "no") << "\n";}
const string YESNO[2] = {"NO", "YES"};//上
const string YesNo[2] = {"No", "Yes"};
const string yesno[2] = {"no", "yes"};
void print() { cout << '\n'; }
template<typename T>//print(a,b,c,...)
void print(const T &t) { cout << t << '\n'; }
template<typename Head, typename... Tail>
void print(const Head &head, const Tail &... tail) {
    cout << head << ' ';
    print(tail...);
}
//-----
const int MOD  = 998244353; //1+119×2^23
const int INF = 1e9+7;
//-search-
using Graph = vector<vector<int>>;
int dx[8]={1,0,-1,0,1,1,-1,-1};
int dy[8]={0,-1,0,1,-1,1,1,-1};

/*↓↓↓ CODES ↓↓↓*/
/*cin してないやつは愚か*/
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    if(a < b){
        int s = b;
        b = a;
        a = s;
        s = d;
        d = c;
        c = s;
    }
    int sum = a % b;

    int e = c - d;
    rep(i,(sum*b)+1){
        if(e % b == 0){
            cout << c + (i * a);
            return 0;
        }
        e += sum;
    }
}