include

include

include

include

include

include

int main() {

int n, k, rq, cq;

scanf("%d%d", &n, &k);
scanf("%d%d", &rq, &cq);

int right = n - cq;
int left = cq - 1;
int up = n - rq;
int down = rq - 1;

int leftup, leftdown, rightup, rightdown;

if (left < up) {
    leftup = left;
} 
else {
    leftup = up;
}

if (left < down) {
    leftdown = left;
} 
else {
    leftdown = down;
}

if (right < up) {
    rightup = right;
} 
else {
    rightup = up;
}

if (right < down) {
    rightdown = right;
} 
else {
    rightdown = down;
}

for (int i = 0; i < k; ++i) {

    int ro, co;
    scanf("%d%d", &ro, &co);

    if (rq == ro && cq > co) {
        if (cq - co - 1 < left) left = cq - co - 1;
    } 
    else if (rq == ro && cq < co) {
        if (co - cq - 1 < right) right = co - cq - 1;
    } 
    else if (cq == co && rq < ro) {
        if (ro - rq - 1 < up) up = ro - rq - 1;
    } 
    else if (cq == co && rq > ro) {
        if (rq - ro - 1 < down) down = rq - ro - 1;
    } 
    else if (co < cq && ro > rq && (cq - co) == (ro - rq)) {
        if (ro - rq - 1 < leftup) leftup = ro - rq - 1;
    } 
    else if (co < cq && rq > ro && (cq - co) == (rq - ro)) {
        if (cq - co - 1 < leftdown) leftdown = cq - co - 1;
    } 
    else if (co > cq && rq > ro && (co - cq) == (rq - ro)) {
        if (co - cq - 1 < rightdown) rightdown = co - cq - 1;
    } 
    else if (co > cq && rq < ro && (co - cq) == (ro - rq)) {
        if (ro - rq - 1 < rightup) rightup = ro - rq - 1;
    }
}

printf("%d", right + left + up + down + leftup + leftdown + rightup + rightdown);
return 0;

}