#include <bits/stdc++.h>
using namespace std;

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

#define V2(T, x, y) (x, vector<T>(y, 0))
template<typename T> struct Sum2 {
	typedef vector<vector<T>> A;
	// A s;
	int X, Y;
	Sum2() { X = Y = -1; }
	Sum2(A & p) { init(p); }
	void init(A & s, int X, int Y) {
		// X = s.size();
		// Y = s[0].size();
		// s = A V2(T, X + 1, Y + 1);
		dec1(x, X) { dec1(y, Y) { s[x][y]  = s[x - 1][y - 1]; } }
		inc(x, X + 1) { s[x][0] = 0; }
		inc(y, Y + 1) { s[0][y] = 0; }
		inc1(x, X) { inc1(y, Y) { s[x][y] += s[x - 1][y    ]; } }
		inc1(x, X) { inc1(y, Y) { s[x][y] += s[x    ][y - 1]; } }
	}
	T sum(A & s, int xl, int xh, int yl, int yh) { // [xl, xh) × [yl, yh)
		/*
		assert(inII(xl, 0, X));
		assert(inII(xh, 0, X + 1));
		assert(inII(yl, 0, Y));
		assert(inII(yh, 0, Y + 1));
		assert(xl <= xh);
		assert(yl <= yh);
		*/
		return s[xh][yh] - s[xh][yl] - s[xl][yh] + s[xl][yl];
	}
};

// ----

LL n, k, p, x[4000], y[4000];
vector<vector<LL>> a V2(LL, 4001, 4001);
vector<vector<LL>> b V2(LL, 4001, 4001);
Sum2<LL> sa, sb;

LL f(int i, int j, int l) {
	return sb.sum(b, i, l, 0, j + n - i) - sa.sum(a, i, l, 0, j);
}

int main() {
	cin >> n >> k >> p;
	inc(i, k) { cin >> x[i] >> y[i]; x[i]--; y[i]--; }
	
	inc(i, n) {
	incII(j, 0, i) {
		a[i][j] = n;
	}
	}
	queue<pair<int, int>> q;
	inc(i, k) {
		a[x[i]][y[i]] = 0;
		q.push(MP(x[i], y[i]));
	}
	while(! q.empty()) {
		auto e = q.front(); q.pop();
		int dx[6] = { +1,  0, -1,  0, +1, -1 };
		int dy[6] = {  0, +1,  0, -1, +1, -1 };
		inc(l, 6) {
			int xx = e.FI + dx[l];
			int yy = e.SE + dy[l];
			if(inID(xx, 0, n) && inID(yy, 0, n)) { } else { continue; }
			if(setmin(a[xx][yy], a[e.FI][e.SE] + 1)) { q.push(MP(xx, yy)); }
		}
	}
	
	inc(i, n) {
	incII(j, 0, i) {
		b[i][j + (n - 1 - i)] = a[i][j];
	}
	}
	
	sa.init(a, n, n);
	sb.init(b, n, n);
	
	LL ans = 0;
	inc1(v, n) { int L = n;
	dec(j, v) {
		int i = n - v + j;
		while(f(i, j, L) >= p) { L--; }
		ans += n - L;
	}
	}
	
	cout << ans << endl;
	
	return 0;
}