import java.util.*; 
import java.io.*;
import java.math.*;
import java.util.stream.*;
import java.util.function.*;

class Main implements Runnable {

    public void solve(){    
        int A = in.nextInt() , B = in.nextInt();
        int a = in.nextInt() , b = in.nextInt();
        for(int i = 0 ; i <= 100000000 ; i ++) {
            if((i % A == a) && (i % B == b)) {
                print(i);
                return;
            }
        }
    }

    public record Pair<T,S> (T fi , S se) { 
        public String toString() { 
            return "("+fi+","+se+")";
        }
    }

    public record Trio<T,S,U>(T fi , S se , U th) { 
        public String toString() { 
            return "("+fi+","+se+","+th+")";
        }
    }

    public PrintWriter out = new PrintWriter(System.out);
    public In in = new In();
    public static final int mod7 = 1000000007;
    public static final int mod9 = 998244353;
    public static final int  inf = (1  << 30);
    public static final long lnf = (1L << 60);
    public static final String yes = "Yes";
    public static final String no  = "No" ;
    public static final int [] dy4 = {-1,0,1,0};
    public static final int [] dx4 = {0,1,0,-1};
    public static final int [] dy8 = {-1,-1,-1,0,1,1,1,0};
    public static final int [] dx8 = {-1,0,1,1,1,0,-1,-1};

    public boolean isOver(int y , int x , int h , int w) { 
        return y < 0 || x < 0 || y >= h || x >= w ;
    }

    public void swap(int [] array , int l , int r) { 
        int tmp = array[l] ; 
        array[l] = array[r] ; 
        array[r] = tmp ; 
    }

    public void swap(long [] array , int l , int r) { 
        long tmp = array[l] ; 
        array[l] = array[r] ; 
        array[r] = tmp ; 
    }
    
    public String swap(String string , int l , int r) { 
        StringBuilder m = new StringBuilder(string) ;
        m.setCharAt(l, string.charAt(r)); m.setCharAt(r, string.charAt(l)); 
        return m.toString(); 
    }

    public String binarytoString(int a , int len) { 
        String b = Integer.toBinaryString(a); 
        while(b.length() < len) b = "0" + b ; 
        return b ; 
    }

    public String binarytoString(long a , int len) { 
        String b = Long.toBinaryString(a); 
        while(b.length() < len) b = "0" + b ; 
        return b ; 
    }

    public <T extends Comparable<T>> int LowCountClosed(List<T> A , T key) { 
        return upperbound(A, key); 
    }

    public <T extends Comparable<T>> int LowCountOpen(List<T> A , T key) { 
        return lowerbound(A, key); 
    }

    public <T extends Comparable<T>> int HighCountClosed(List<T> A , T key) { 
        return A.size() - lowerbound(A, key); 
    }

    public <T extends Comparable<T>> int HighCountOpen(List<T> A , T key) { 
        return A.size() - upperbound(A, key); 
    }
    // [)
    public <T extends Comparable<T>> int CountClosedOpen(List<T> A, T a, T b) {
        return lowerbound(A, b) - lowerbound(A, a);
    }
    // []
    public <T extends Comparable<T>> int CountClosedClosed(List<T> A, T a, T b) {
        return upperbound(A, b) - lowerbound(A, a);
    }
    // (]
    public <T extends Comparable<T>> int CountOpenClosed(List<T> A, T a, T b) {
        return upperbound(A, b) - upperbound(A, a);
    }
    // ()
    public <T extends Comparable<T>> int CountOpenOpen(List<T> A, T a, T b) {
        return lowerbound(A, b) - upperbound(A, a);
    }

    private <T extends Comparable<T>> int lowerbound(List<T> A, T key) {
        int left = 0 , right = A.size();
        while (left < right) {
            int mid = (left + right) / 2;
            if (A.get(mid).compareTo(key) < 0) left = mid + 1;
            else right = mid;
        }
        return right;
    }

    private <T extends Comparable<T>> int upperbound(List<T> A, T key) { 
        int left = 0 , right = A.size();
        while (left < right) {
            int mid = (left + right) / 2;
            if (A.get(mid).compareTo(key) <= 0) left = mid + 1;
            else right = mid;
        }
        return right;
    }

    public Integer [] toInteger(int [] a) {
        return Arrays.stream(a).boxed().toArray(Integer[]::new);
    }

    public Long [] toLong(long [] a) {
        return Arrays.stream(a).boxed().toArray(Long[]::new);
    }

    public Double [] toDouble(double [] a) {
        return Arrays.stream(a).boxed().toArray(Double[]::new);
    }

    public int [] toIntArray(Collection<Integer> collection) {
        int [] array = new int[collection.size()];
        int cur = 0 ;
        for(int value : collection) array[cur++] = value ;
        return array ;
    }

    public long [] toLongArray(Collection<Long> collection) {
        long [] array = new long[collection.size()];
        int cur = 0 ;
        for(long value : collection) array[cur++] = value ;
        return array ;
    }

    public <T> List<T> ArrayList(T [] a) { 
        return Arrays.stream(a).collect(Collectors.toCollection(ArrayList::new));
    }

    public <T> HashSet<T> HashSet(T [] a) { 
        return Arrays.stream(a).collect(Collectors.toCollection(HashSet::new));
    }

    public <T> TreeSet<T> TreeSet(T [] a) { 
        return Arrays.stream(a).collect(Collectors.toCollection(TreeSet::new));
    }

    public <T> Deque<T> Deque(T [] a) { 
        return Arrays.stream(a).collect(Collectors.toCollection(ArrayDeque::new));
    }

    public <T> PriorityQueue<T> PriorityQueue(T [] a) { 
        return Arrays.stream(a).collect(Collectors.toCollection(PriorityQueue::new));
    }

    public <T> List <T> [] ArrayList(int n) { 
        @SuppressWarnings("unchecked")
        List<T> [] G = new ArrayList[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new ArrayList<>();
        return G ; 
    }

    public <T> HashSet <T> [] HashSet(int n) { 
        @SuppressWarnings("unchecked")
        HashSet<T> [] G = new HashSet[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new HashSet<>()  ;
        return G ; 
    }

    public <T> TreeSet <T> [] TreeSet(int n) { 
        @SuppressWarnings("unchecked")
        TreeSet<T> [] G = new TreeSet[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeSet<>()  ; 
        return G ; 
    }

    public <T> TreeSet <T> [] TreeSet(int n , Comparator<? super T> comparator) { 
        @SuppressWarnings("unchecked")
        TreeSet<T> [] G = new TreeSet[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeSet<>(comparator)  ;
        return G ; 
    }

    public <T> Deque <T> [] Deque(int n) { 
        @SuppressWarnings("unchecked")
        Deque<T> [] G = new ArrayDeque[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new ArrayDeque<>(); 
        return G ; 
    }

    public <T> PriorityQueue <T> [] PriorityQueue(int n) { 
        @SuppressWarnings("unchecked")
        PriorityQueue<T> [] G = new PriorityQueue[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new PriorityQueue<>(); 
        return G ; 
    }

    public <T> PriorityQueue <T> [] PriorityQueue(int n , Comparator<? super T> comparator) { 
        @SuppressWarnings("unchecked")
        PriorityQueue<T> [] G = new PriorityQueue[n]; 
        for(int i = 0 ; i < n ; i ++ ) G[i] = new PriorityQueue<>(comparator); 
        return G ; 
    }

    public <K,V> HashMap <K,V> [] HashMap(int n) { 
        @SuppressWarnings("unchecked")
        HashMap<K,V> [] G = new HashMap[n];
        for(int i = 0 ; i < n ; i ++ ) G[i] = new HashMap<>()  ;
        return G ; 
    }

    public <K,V> TreeMap <K,V> [] TreeMap(int n) { 
        @SuppressWarnings("unchecked")
        TreeMap<K,V> [] G = new TreeMap[n];
        for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeMap<>()  ;
        return G ;
    }

    public <K,V> TreeMap <K,V> [] TreeMap(int n , Comparator<? super K> comparator) { 
        @SuppressWarnings("unchecked")
        TreeMap<K,V> [] G = new TreeMap[n];
        for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeMap<>(comparator)  ;
        return G ; 
    }

    //---------------------------------------------------------------------------------------//

    @SuppressWarnings("unchecked")
    public <T> void print(T ... data) {
        StringBuilder pr = new StringBuilder();
        for(var temp : data) pr.append(temp+" ");
        out.println(pr.toString());
        out.flush();
    }

    public void print(String [][] array) {
        StringBuilder pr = new StringBuilder();
        for(var temp : array) {
            for(var data : temp) {
                pr.append(data+" ");
            }
            pr.append("\n");
        }
        if(0 < pr.length()) pr.deleteCharAt(pr.length() - 1);
        out.println(pr.toString());
        out.flush();
    }

    public void print(char [][] array) {
        StringBuilder pr = new StringBuilder();
        for(var temp : array) {
            for(var data : temp) {
                pr.append(data);
            }
            pr.append("\n");
        }
        if(0 < pr.length()) pr.deleteCharAt(pr.length() - 1);
        out.println(pr.toString());
        out.flush();
    }

    public <T> void print(Collection<T> collection) {
        StringBuilder pr = new StringBuilder();
        for(T data : collection) pr.append(data +" ");
        out.println(pr.toString());
        out.flush();
    }   

    public static void main(String ... args) {
        new Thread(null, new Main(), "", Runtime.getRuntime().maxMemory()).start(); 
    }

    public void run() {   
        solve();
        out.flush();
    }

}

class In {

    private final InputStream in = System.in;
    private final Scanner sc = new Scanner(System.in);
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() { 
        if (hasNextByte()) return buffer[ptr++]; else return -1;
    }

    private static boolean isPrintableChar(int c) { 
        return 33 <= c && c <= 126;
    }

    private  boolean hasNext() { 
        while(hasNextByte() && !isPrintableChar(buffer[ptr])) {
            ptr++; 
        }
        return hasNextByte();
    }
    
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() { 
        return Double.parseDouble(next());
    }

    public char nextChar() {
        return next().charAt(0);
    }

    public BigInteger nexBigInteger() {
        return sc.nextBigInteger();
    }

    public int [] nextInt(int n) {
        int [] array = new int[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextInt();
        }
        return array ;
    }

    public int [][] nextInt(int n , int m) {
        int [][] array = new int[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextInt(m);
        }
        return array ;
    }

    public long [] nextLong(int n) {
        long [] array = new long[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextLong();
        }
        return array ;
    }

    public long [][] nextLong(int n , int m) {
        long [][] array = new long[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextLong(m);
        }
        return array ;
    }

    public double [] nextDouble(int n) {
        double [] array = new double[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextDouble();
        }
        return array ;
    }
    
    public String [] next(int n) {
        String [] array = new String[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = next();
        }
        return array ;
    }

    public String [][] next(int n , int m) {
        String [][] array = new String[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = next(m);
        }
        return array ;
    }

    public char [] nextChar(int n) {
        char [] array = new char[n];
        String string = next() ;
        for(int i = 0 ; i < n ; i ++) {
            array[i] = string.charAt(i);
        }
        return array ;
    }

    public char [][] nextChar(int n , int m) {
        char [][] array = new char[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextChar(m);
        }
        return array ;
    }

}