#include <cstdio>
using namespace std;
int v[15];

int main()
{
    //FILE *fin, *fout;
    int g,aux,i,nr;
    //fin=fopen("spell.in","r");
    scanf("%d%d%d%d",&v[1],&v[2],&v[3],&v[4]);
    //fclose(fin);
    g=0;
    while(g==0){
      g=1;
      for(i=1;i<=3;++i){
        if(v[i]>v[i+1]){
          g=0;
          aux=v[i];
          v[i]=v[i+1];
          v[i+1]=aux;
        }
      }
    }
    nr=v[1]*v[2]+v[4]*v[3];
    //fout=fopen("spell.out","w");
    printf("%d",nr);
    //fclose(fout);
    return 0;
}