#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
int n, k;
ll p;
int x[4040], y[4040];
int a[4040][4040];
int dx[6]={1, -1, 0, 0, 1, -1}, dy[6]={0, 0, 1, -1, 1, -1};
int s[4040][4040], s2[4040][4040];
int sum(int i, int j, int d){
    return s2[i+d][j+d]-s2[i][j]-s[i+d][j]+s[i][j];
}
int main()
{
    cin>>n>>k>>p;
    const int INF=1e9;
    for(int i=0; i<n; i++) for(int j=0; j<=i; j++) a[i][j]=INF;
    queue<P> que;
    for(int i=0; i<k; i++){
        cin>>x[i]>>y[i]; x[i]--; y[i]--;
        que.push({x[i], y[i]});
        a[x[i]][y[i]]=0;
    }
    while(!que.empty()){
        P p=que.front(); que.pop();
        int s=p.first, t=p.second;
        for(int i=0; i<6; i++){
            int s1=s+dx[i], t1=t+dy[i];
            if(!(s1>=0 && t1>=0 && s1<n && t1<=s1)) continue;
            if(a[s1][t1]>a[s][t]+1){
                a[s1][t1]=a[s][t]+1;
                que.push({s1, t1});
            }
        }
    }
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
            s[i+1][j+1]=s[i][j+1]+s[i+1][j]-s[i][j]+a[i][j];
        }
    }
    for(int i=0; i<n; i++){
        for(int j=0; j<=i; j++){
            s2[i+1][j+1]=s2[i][j]+s[i+1][j+1]-s[i][j+1];
        }
    }
    ll ans=0;
    for(int i=0; i<n; i++){
        for(int j=0; j<=i; j++){
            int l=0, r=n-i+1;
            while(r-l>1){
                int m=(l+r)>>1;
                if(sum(i, j, m)>=p) r=m;
                else l=m;
            }
            ans+=n-i+1-r;
        }
    }
    cout<<ans<<endl;
	return 0;
}