// need
#include <iostream>
#include <algorithm>

// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
//#include <complex>
//#include <deque>
#include <valarray>

// stream
//#include <istream>
//#include <sstream>
//#include <ostream>
#include <fstream>

// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int i=0; i<n; ++i){MACRO_VEC_ROW_Scan(i, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;

// output
#define OUT(d) std::cout<<(d);
#define FOUT(n, d) std::cout<<std::fixed<<std::setprecision(n)<<(d);
#define SOUT(n, c, d) std::cout<<std::setw(n)<<std::setfill(c)<<(d);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(i, n) std::cout<<(i + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(d) {std::cerr << #d << "\t:" << (d) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}

// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=int(n)-1;i>=0;--i)
#define FORLL(i, a, b) for(ll i=ll(a);i<ll(b);++i)
#define RFORLL(i, a, b) for(ll i=ll(b)-1;i>=ll(a);--i)
#define REPLL(i, n) for(ll i=0;i<ll(n);++i)
#define RREPLL(i, n) for(ll i=ll(n)-1;i>=0;--i)
#define IN(a, x, b) (a<=x && x<b)
template<typename T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
template<typename T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
#define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
#define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }

// test
template<class T> std::vector<std::vector<T>> VV(int n, int m, T init = T()) {
	return std::vector<std::vector<T>>(n, std::vector<T>(m, init));
}
template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
//#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = 1 << 30;                          // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-9;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;

template<class T, size_t N> void FILL(T(&a)[N], const T& val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T& val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T>& a, const T& val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>>& a, const T& val) { for (auto& b : a) FILL(b, val); }

// ------------>8------------------------------------->8------------

signed main() {
	INIT;

	VAR(int, n, k, p);
	VEC_ROW(int, k, x, y);

	if (n == 1) {
		OUT(!p)BR;
		return 0;
	}

	int N = n * (n + 1) / 2;
	std::vector<std::vector<int>> g(N + 1);
	auto POS = [](int i, int j) { return i * (i + 1) / 2 + j; };
	REP(i, n - 1) REP(j, i + 1) {
		g[POS(i, j)].emplace_back(POS(i + 1, j));
		g[POS(i, j)].emplace_back(POS(i + 1, j + 1));
		if (j > 0) g[POS(i, j)].emplace_back(POS(i, j - 1));

		g[POS(i + 1, j)].emplace_back(POS(i, j));
		g[POS(i + 1, j + 1)].emplace_back(POS(i, j));
		if (j > 0) g[POS(i, j - 1)].emplace_back(POS(i, j));
	}

	REP(i, k) {
		--x[i]; --y[i];
		g[N].emplace_back(POS(x[i], y[i]));
	}

	std::vector<int> dist(N + 1, INFINT);
	dist[N] = -1;
	std::queue<int> que({N});
	while (!que.empty()) {
		int now = que.front(); que.pop();
		for (auto to : g[now]) {
			if (dist[to] > dist[now] + 1) {
				dist[to] = dist[now] + 1;
				que.push(to);
			}
		}
	}

	std::vector<int> A(N), B(N), C(N), dp(N, INFINT);
	{ // A
		REP(j, n) A[POS(n - 1, j)] = dist[POS(n - 1, j)];
		REP(j, n - 1) A[POS(n - 2, j)] = dist[POS(n - 1, j)] + dist[POS(n - 1, j + 1)] + dist[POS(n - 2, j)];

		RREP(i, n - 2) REP(j, i + 1) {
			A[POS(i, j)] = A[POS(i + 1, j)] + A[POS(i + 1, j + 1)] - A[POS(i + 2, j + 1)] + dist[POS(i, j)];
		}
	}

	{ // B
		B[POS(n - 1, 0)] = A[POS(n - 1, 0)];
		FOR(j, 1, n) B[POS(n - 1, j)] = B[POS(n - 1, j - 1)] + dist[POS(n - 1, j)];

		RREP(i, n - 1) {
			B[POS(i, 0)] = A[POS(i, 0)];
			FOR(j, 1, i + 1) {
				B[POS(i, j)] = B[POS(i, j - 1)] + B[POS(i + 1, j + 1)] - B[POS(i + 1, j)] + dist[POS(i, j)];
			}
		}
	}

	{ // C
		C[POS(n - 1, n - 1)] = A[POS(n - 1, n - 1)];
		RREP(j, n - 1) C[POS(n - 1, j)] = C[POS(n - 1, j + 1)] + dist[POS(n - 1, j)];

		RREP(i, n - 1) {
			C[POS(i, i)] = A[POS(i, i)];
			RREP(j, i) {
				C[POS(i, j)] = C[POS(i, j + 1)] + C[POS(i + 1, j)] - C[POS(i + 1, j + 1)] + dist[POS(i, j)];
			}
		}
	}

	auto calcSub = [&](int i, int j, int b) {
		if (i == b) return dist[POS(i, j)];
		if (b == n - 1) return A[POS(i, j)];
		int l = j, r = j + (b - i) + 1;
		return A[POS(i, j)] - (B[POS(b + 1, r)] + C[POS(b + 1, l)] - B[POS(b + 1, b + 1)]);
	};

	int ans = 0;
	RREP(i, n) REP(j, i + 1) {
		if (i == n - 1) {
			if (A[POS(i, j)] >= p) {
				++ans;
				dp[POS(i, j)] = n - 1;
			}
		}
		else {
			dp[POS(i, j)] = std::min(dp[POS(i + 1, j)], dp[POS(i + 1, j + 1)]);
			int sum = A[POS(i, j)];
			int& b = dp[POS(i, j)];
			if (b == INFINT) {
				if (sum >= p) b = n - 1;
				else continue;
			}
			if (b < n - 1) {
				int l = j, r = j + (b - i);
				sum -= B[POS(b + 1, r)] + C[POS(b + 1, l)] - B[POS(b + 1, b + 1)];
			}
			while (i < b && sum >= p) {
				sum = calcSub(i, j, --b);
			}
			CHMAX(b, i);
			while (b < n) {
				sum = calcSub(i, j, b);
				if (sum >= p) break;
				else ++b;
			}
			ans += n - b;
		}
	}
	OUT(ans)BR;
	return 0;
}