#include <cstdio>
int dx[] = { 0, 1, 0, -1, 1, -1 };
int dy[] = { 1, 0, -1, 0, -1, 1 };
int N, K, x, y, l, r, qx[8002009], qy[8002009], v[4009][4009], sx[4009][4009], sy[4009][4009]; long long X;
int main() {
	scanf("%d %d %lld", &N, &K, &X);
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < N - i; j++) {
			v[i][j] = -1;
		}
	}
	for (int i = 0; i < K; i++) {
		scanf("%d %d", &x, &y), x = x - y, y--;
		if (v[x][y] == -1) v[x][y] = 0, qx[r] = x, qy[r++] = y;
	}
	while (l != r) {
		x = qx[l], y = qy[l++];
		for (int i = 0; i < 6; i++) {
			int tx = x + dx[i], ty = y + dy[i];
			if (0 <= tx && tx < N && 0 <= ty && ty < N && 0 <= tx + ty && tx + ty < N && v[tx][ty] == -1) {
				v[tx][ty] = v[x][y] + 1;
				qx[r] = tx, qy[r++] = ty;
			}
		}
	}
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < N - i; j++) {
			sx[i][j + 1] = sx[i][j] + v[i][j];
			sy[i][j + 1] = sy[i][j] + v[j][i];
		}
	}
	long long ret = 0;
	for (int i = 0; i < N; i++) {
		int cx = i + 1; long long cs = 0;
		for (int j = 0; j <= i; j++) {
			while (cx != 0) {
				int delta = sy[cx - 1][i - cx + 2] - sy[cx - 1][j];
				if (cs + delta >= X) break;
				cs += delta;
				cx--;
			}
			ret += cx;
			cs -= sx[j][i - j + 1] - sx[j][cx];
		}
	}
	printf("%lld\n", ret);
	return 0;
}