#include <iostream>
using namespace std;
int main() {
int n1,k1,n2,k2;
cin>>n1>>k1>>n2>>k2;
cout<<(n1*k1)+(n2*k2);
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKaW50IG1haW4oKSB7CmludCBuMSxrMSxuMixrMjsKY2luPj5uMT4+azE+Pm4yPj5rMjsKY291dDw8KG4xKmsxKSsobjIqazIpOwoKCXJldHVybiAwOwp9