#include <stdio.h>

using namespace std;
FILE *f=fopen("piatra.in","r");
FILE *g=fopen("piatra.out","w");

int m,n,l,c,nr,ss,s,s1,p,pp;
int main()
{
    fscanf(f,"%d%d%d%d",&n,&m,&l,&c);
   nr=(l+c-2);

   if (nr<=n-2)s=nr*(nr+1)/2;
   else ss=(n-1)*(n)/2;
   if (nr>m-1)
   {
       s=ss+(n*(m-n+1));
       p=nr-m+1;
       pp=n-p;
       s1=((n-1)*n/2)-(pp*(pp+1)/2);
       s+=s1;

   }
   else if (nr<=m-1 && nr>n-2)s=ss+n*(nr-n+1);

   if (nr%2==0)
    {
      if (c<=m/2)s+=c;
       else s+=(m-c)+1;
    }
   else
   {
     if (l<=n/2)s+=l;
     else s+=(n-l)+1;
   }
   fprintf(g,"%d",s);


    fclose(g);
    return 0;
}