#include<bits/stdc++.h>

using namespace std;

#define ll long long

#define pb push_back

#define mem(a,b) memset((a),(b),sizeof(a))

const ll INF=1e18;

ll c1,c2,x,y;

bool check(ll v)

{

    ll f1=v/x;//整除x

    ll f2=v/y;///整除y

    ll b=v/(x*y);//都整除

    ll _f1=f1-b;//只整除x

    ll _f2=f2-b;//只整除y

    ll o=v-_f1-_f2-b;//都不整除

    ll t1=c1-_f2;//还需要的个数

    if(t1<=)t1=;

    ll t2=c2-_f1;//还需要的个数

    if(t2<=)t2=;

    return (t1+t2<=o);

}

int main()

{

    cin>>c1>>c2>>x>>y;

    ll l=,r=INF,m;

    while(l<r)

    {

        m=(l+r)>>;

        if(check(m))r=m;

        else l=m+;

    }

    m=(l+r)>>;

    cout<<m<<endl;

    return ;

}