#include<iostream>


int mod(int n,int b){
    return (n%b<0)?(b+n%b):(n%b);
}

using namespace std;
int main(){
    int b0,c0,b1,c1;
    cin>>b0>>c0>>b1>>c1;
    
    for(int i=0;i<b0*b1;i++){
        if(mod(i,b0)==mod(c0,b0)&&mod(i,b1)==mod(c1,b1)){
            cout<<i<<endl;
            return 0;
        }
    }
    cout<<"NaN"<<endl;
    return 0;
}