#pragma GCC optimize("Ofast,unroll-loops")
#include<bits/stdc++.h>
#define int   long long
#define ll long long
#define down cout<<'\n';
#define debug cout<<" cucuucucuuu",down
#define NHP     ios_base::sync_with_stdio(0);cout.tie(0);cin.tie(0);
#define modwwe  int t;cin>>t; while(t--)
#define bit(i,j) (i>>j&1)
#define sobit(a) __builtin_popcountll(a)
#define task "test"
#define fin(x) freopen(x".inp","r",stdin)
#define fou(x) freopen(x".out","w",stdout)
#define pb push_back
#define mask(k) (1<<k)
#define mp make_pair
#define checktime   cerr << (double)clock() / CLOCKS_PER_SEC * 1000  << " ms";
using namespace std;
#define getchar_unlocked getchar

inline int scan()
{
    char c = getchar_unlocked();
    int x = 0;
    while (c < '0' || c > '9')
    {
        c = getchar_unlocked();
    }
    while (c >= '0' && c <= '9')
    {
        x = (x << 1) + (x << 3) + c - '0';
        c = getchar_unlocked();
    }
    return x;
}
void phongbeo();
const int inf = 1e16;
const ll mod2 = 1e9+7;
const int  mod1 = 998244353;
const ll base=67;
int add(int x,int y)
{
    if(x+y>=mod2) x-=mod2;
    if(x+y<0)x+=mod2;
    return x+y;
}
struct icd
{
    long double a;
    int b;
};
struct ib
{
    int a;
    int b;
};
struct ic
{
    ll a;
    int  b, c;
};
struct id
{
    int a, b, c, d;
};
struct ie
{
    int a, b, c, d, e;

};
int n, m, s1, s2, s4, s3, sf, k, s5, s6, mx, s7, s8, s9, mx2, res, dem2 = 0, dem = 0, s33, dem3, dem4, mid, l2, r2, center;
int  i, s10, s12,k1,k2,k3,s11,lim,w,l,r ;
int kk;
int el = 19;
main()
{
    if(fopen(task".inp","r"))
    {
        fin(task);
        fou(task);
    }
    NHP
    ///  cin>>s1;
    // modwwe
    phongbeo();
//   checktime
}
int dl[4001];
int dr[4001];
bool c[4001][4001];
vector<int> v[4002];
int b[4001][4001];
int a[4001][4001];
struct skibidi
{
    int bit[4001];
    void upd(int x,int y)
    {
        for(x; x; x-=x&-x)
            bit[x]+=y;
    }
    int get(int x)
    {
        int s=0;
        for(x; x<=n; x+=x&-x)
            s+=bit[x];
        return s;
    }
    void reset()
    {
        for(int i=1; i<=n; i++)
            bit[i]=0;
    }
} fen;
void phongbeo()
{
    cin>>n>>m>>lim>>k;
    for(int i=1; i<=k; i++)
        cin>>l>>r,c[l][r]=1;
    for(int i=1; i<=n; i++)
        dr[i]=m+1;
    for(int i=1; i<=m; i++)
        dl[i]=n+1;
/// build .###
///       #xx#
///       #xx#
///       #xx.
    for(int i=n; i>=1; --i)
        for(int j=m; j>=1; --j)
        {
            if(c[i][j])
            {
                dl[j]=min(dl[j],i);
                dr[i]=min(dr[i],j);
            }
            s4=min(dl[j]-i,dr[i]-j);
            a[i][j]=-1;
            if(i+s4<=n&&j+s4<=m)
                a[i][j]=s4;
        }
    for(int i=1; i<=n; i++)
        dr[i]=0;
    for(int i=1; i<=m; i++)
        dl[i]=0;
    for(int i=1; i<=n; ++i)
        for(int j=1; j<=m; ++j)
        {
            if(c[i][j])
            {
                dl[j]=max(dl[j],i);
                dr[i]=max(dr[i],j);
            }
            b[i][j]=i-min(i-dl[j],j-dr[i])+1;
        }
    s4=0;
    for(int f=1-n; f<=m-1; f++)
    {
        for(int  i=max(1ll,1-f); i<=n; i++)
        {
            int j=f+i;
            if(f+i>=1&&f+i<=m)
            {
                fen.upd(i,1);
                if(a[i][j]!=-1)
                {
                    v[i+a[i][j]].pb(i);
                }
            }
            for(auto x:v[i])
                fen.upd(x,-1);
            vector<int>().swap(v[i]);
            if(j>=1&&j<=m)
            {
                if(i-b[i][j]+1>=lim)
                {
                    s4+=fen.get(b[i][j]);
                    s4-=fen.get(i-lim+2);
                }
            }
        }
        fen.reset();
    }
    cout<<s4;
}