#include <bits/stdc++.h>
using namespace std;
int xja[8] = {-2,-1,1,2,2,1,-1,-2};
int yja[8] = {1,2,2,1,-1,-2,-2,-1};
int main(){
int a,b,c,d,xl=0,yl=0;
cin>>a>>b>>c>>d;
long long m[21][21] = {0};
int z[21][21] = {0};
z[0][0] = 1;
for(int i=0;i<=a;i++){
m[i][0] = 1;
}
for(int i=0;i<=b;i++){
m[0][i] = 1;
}
for(int i=0;i<8;i++){
xl = c+xja[i];
yl = d+yja[i];
if(xl>=0 && xl<=a && yl>=0 && yl<=b){
m[xl][yl] = -1;
}
}
m[c][d] = -1;
for(int i=1;i<=a;i++){
for(int j=1;j<=b;j++){
if(m[i][j]!=-1 && z[i][j]==0){
z[i][j] = 1;
if((m[i-1][j]==-1 && m[i][j-1]!=-1) || (m[i-1][j]!=-1 && m[i][j-1]==-1)){
m[i][j] = m[i-1][j]+m[i][j-1]+1;
}else if(m[i-1][j]==-1 && m[i][j-1]==-1){
m[i][j] = m[i-1][j]+m[i][j-1]+2;
}else{
m[i][j] = m[i-1][j]+m[i][j-1];
}
}
}
}
cout<<m[a][b];
return 0;
}