import java.util.*;
import java.io.*;
/**
* Created by rajat goyal on 3/19/2017.
*/
public class QueensAttack {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
int k = in.nextInt();
int rq = in.nextInt();
int cq = in.nextInt();
int e = n - cq, north = n - rq, w = cq - 1, s = rq - 1;
int ne = Math.min(north, e), se = Math.min(s, e), nw = Math.min(north, w), sw = Math.min(s, w);
for (int a0 = 0; a0 < k; a0++) {
int ro = in.nextInt();
int co = in.nextInt();
int r = ro - rq;
int c = co - cq;
if (r == 0) {
if (c > 0) {
if (c - 1 < e) {
e = c - 1;
}
} else {
if (-c - 1 < w) {
w = -c - 1;
}
}
} else if (c == 0) {
if (r > 0) {
if (r - 1 < north) {
north = r - 1;
}
} else {
if (-r - 1 < s) {
s = -r - 1;
}
}
} else if (r == c) {
if (r > 0) {
if (r - 1 < ne) {
ne = r - 1;
}
} else {
if (-r - 1 < sw) {
sw = -r - 1;
}
}
} else if (r == -c) {
if (r > 0) {
if (r - 1 < nw) {
nw = r - 1;
}
} else {
if (-r - 1 < se) {
se = -r - 1;
}
}
}
}
int count = e + ne + north + nw + w + s + se + sw;
System.out.println(count);
}
}