#include<bits/stdc++.h>
using namespace std;
const int N = 4040;
int a[N][N];
int l[N][N],r[N][N],dn[N][N],up[N][N];
vector<int>e[N];
int b[N];
int n,m,len,p;
int lowbit(int x){
	return x&-x;
}
void add(int x,int v){
	for(;x<=m;x+=lowbit(x))b[x]+=v;
}
int query(int x){
	int res = 0;
	for(;x;x-=lowbit(x))res+=b[x];
	return res;
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin>>n>>m>>len>>p;
	for(int i = 1;i<=p;i++){
		int x,y;
		cin>>x>>y;
		a[x][y] = 1;
	}
	for(int i = 1;i<=n;i++){
		for(int j = 1;j<=m;j++){
			if(!a[i][j]){
				l[i][j] = l[i][j-1]+1;
				up[i][j] = up[i-1][j]+1;
			}
		}
	}
	for(int i = n;i>=1;i--){
		for(int j = m;j>=1;j--){
			if(!a[i][j]){
				r[i][j] = r[i][j+1]+1;
				dn[i][j] = dn[i+1][j]+1;
			}
		}
	}

	for(int i = 1;i<=n;i++){
		for(int j = 1;j<=m;j++){
			l[i][j] = min(l[i][j],dn[i][j]);
			r[i][j] = min(r[i][j],up[i][j]);
		}
	}
	long long ans = 0;
	for(int s = 2;s<=n+m;s++){
		int fk = 1,dk = s-1;
		if(dk>m)fk = s-m,dk = m;
		for(int x = fk,y = dk;x<=n&&y>=1;x++,y--){
			e[y-l[x][y]].push_back(y);
			add(y,1);
		}
		for(int x = fk,y = dk;x<=n&&y>=1;x++,y--){
			for(auto v:e[y])add(v,-1);
			if(r[x][y]>=len)ans+=query(y+r[x][y]-1)-query(y+len-2);
		}
		for(int i = 1;i<=m;i++)e[i].clear();
		memset(b,0,sizeof(b));
	}
	cout<<ans;
	return 0;
}