#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define uchar unsigned char

typedef struct long_ {
  uchar l;
  uchar a[100];
} long_;


long x1, x2, y1_, y2, N, M, tmp, j;
long_ s, a;
uchar b[200], c[200];
long i;


uchar gcd(uchar a,uchar b)
{
  while (a != 0 && b != 0) {
    if (a > b)
      a %= b;
    else
      b %= a;
  }
  return (a + b);
}


void mul(long_ *a,long b)
{
  uchar i, c;
  long K = 0;
  uchar FORLIM;

  FORLIM = a->l;
  for (i = 0; i <= FORLIM - 1; i++) {
    c = a->a[i];
    a->a[i] = (b * c + K) % 10;
    K = (b * c + K) / 10;
  }
  while (K != 0) {
    a->l++;
    a->a[a->l - 1] = K % 10;
    K /= 10;
  }
}


void add(long_ *a,long_ *b)

{
  uchar l, c, i;
  uchar k = 0;

  if (a->l > b->l)
    l = a->l;
  else
    l = b->l;
  for (i = 0; i <= l - 1; i++) {
    c = a->a[i];
    a->a[i] = (c + b->a[i] + k) % 10;
    k = (c + b->a[i] + k) / 10;
  }
  a->l = l;
  if (k != 0) {
    a->l++;
    a->a[a->l - 1] = k;
  }
}


void cnk(uchar i1,uchar  j1,uchar  i2,uchar  j2)
{
  long h1 = 0, h2 = 0;
  long i, j;

  for (i = i1 - j1 + 1; i <= i1; i++) {
    h1++;
    b[h1-1] = i;
  }
  for (i = i2 - j2 + 1; i <= i2; i++) {
    h1++;
    b[h1-1] = i;
  }
  for (i = 1; i <= j1; i++) {
    h2++;
    c[h2-1] = i;
  }
  for (i = 1; i <= j2; i++) {
    h2++;
    c[h2-1] = i;
  }
  for (i = 0; i < h1; i++) {
    for (j = 0; j < h2; j++) {
      tmp = gcd(b[i], c[j]);
      b[i] /= tmp;
      c[j] /= tmp;
      if (b[i] == 1) {
       break;
      }
    }
  }
  for (i = 0; i < h1; i++) {
    if (b[i] != 1)
      mul(&a, (long)b[i]);
  }
}


int main(void)
{
  long FORLIM;

  scanf("%ld%ld%ld%ld", &x1, &y1_, &x2, &y2);
  N = abs(x2 - x1) + 1;
  M = abs(y2 - y1_) + 1;
  if (N < M) {
    tmp = N;
    N = M;
    M = tmp;
  }
  FORLIM = N;
  for (i = 0; i < FORLIM; i++) {
    if (i - M >= -1 && N - i >= i - M + 2) {
      memset(&a, 0, sizeof(a));
      a.a[0] = 1;
      a.l = 1;
      cnk((int)(N - 1), (int)i, (int)(N - i - 1), (int)(i - M + 1));
      add(&s, &a);
    }
  }
  for (i = s.l; i >= 1; i--)
    printf("%d", s.a[i-1]);
  putchar('\n');
  return 0;
}