import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


/*
        00      
      10  01    
    20  11  02  
  30  21  12  03
*/

int N, K;
long P;
int[] X, Y;

int[][] D;

void bfs() {
  auto q = new int[N * (N + 1)];
  int qHead, qTail;
  D = new int[][](N, N);
  foreach (x; 0 .. N) foreach (y; 0 .. N) {
    if (x + y < N) {
      D[x][y] = 2 * N;
    }
  }
  foreach (k; 0 .. K) {
    D[X[k]][Y[k]] = 0;
    q[qTail++] = X[k];
    q[qTail++] = Y[k];
  }
  for (; qHead != qTail; ) {
    const x = q[qHead++];
    const y = q[qHead++];
    void update(int xx, int yy) {
      if (D[xx][yy] > D[x][y] + 1) {
        D[xx][yy] = D[x][y] + 1;
        q[qTail++] = xx;
        q[qTail++] = yy;
      }
    }
    if (x + y + 1 < N) {
      update(x + 1, y);
      update(x, y + 1);
    }
    if (x - 1 >= 0) {
      update(x - 1, y + 1);
      update(x - 1, y);
    }
    if (y - 1 >= 0) {
      update(x, y - 1);
      update(x + 1, y - 1);
    }
  }
}

void main() {
  try {
    for (; ; ) {
      N = readInt();
      K = readInt();
      P = readLong();
      X = new int[K];
      Y = new int[K];
      foreach (k; 0 .. K) {
        X[k] = readInt() - 1;
        Y[k] = readInt() - 1;
        X[k] -= Y[k];
      }
      
      bfs();
      
      // rectangle headed at (0, 0)
      auto r = new long[][](N + 1, N + 1);
      foreach (x; 0 .. N) foreach (y; 0 .. N) {
        r[x + 1][y + 1] = r[x][y + 1] + r[x + 1][y] - r[x][y] + D[x][y];
      }
      // D[z][0] + ... + D[0][z]
      auto s = new long[][](N, N + 1);
      foreach (z; 0 .. N) {
        foreach (y; 0 .. z + 1) {
          s[z][y + 1] = s[z][y] + D[z - y][y];
        }
      }
      // triangles headed at (x, 0)
      auto tX = new long[][](N, N + 1);
      foreach (x; 0 .. N) {
        foreach (l; 0 .. N - x) {
          tX[x][l + 1] = tX[x][l] + (s[x + l][l + 1] - s[x + l][0]);
        }
      }
      // triangles headed at (0, y)
      auto tY = new long[][](N, N + 1);
      foreach (y; 0 .. N) {
        foreach (l; 0 .. N - y) {
          tY[y][l + 1] = tY[y][l] + (s[y + l][y + l + 1] - s[y + l][y]);
        }
      }
      
      debug {
        foreach (z; 0 .. N) {
          write(' '.repeat(N - z));
          foreach (y; 0 .. z + 1) {
            write(D[z - y][y], " ");
          }
          writeln();
        }
        writeln("r = ", r);
        writeln("s = ", s);
        writeln("tX = ", tX);
        writeln("tY = ", tY);
      }
      
      long ans;
      /*
      foreach (x; 0 .. N) foreach (y; 0 .. N) {
        if (x + y < N) {
          int lo = 0, hi = N - (x + y) + 1;
          for (; lo + 1 < hi; ) {
            const mid = (lo + hi) / 2;
            const sum = r[x][y] + tX[x][mid + y] + tY[y][mid + x] - tX[0][mid + x + y];
            (sum >= P) ? (hi = mid) : (lo = mid);
          }
          ans += (N - (x + y) + 1) - hi;
        }
      }
      */
      long getSum(int z, int y0, int y1) {
        const l = y1 - y0;
        if (l <= 0) {
          return 0;
        }
        const x = z - (l - 1) - y0;
        const y = y0;
        debug {
          // writeln("getSum ", z, " [", y0, ", ", y1, "); ", l, " ", x, " ", y);
        }
        return r[x][y] + tX[x][l + y] + tY[y][l + x] - tX[0][l + x + y];
      }
      foreach (z; 0 .. N) {
        for (int y0 = 0, y1 = 0; y0 <= z; ++y0) {
          for (; y1 <= z + 1 && (y1 <= y0 || getSum(z, y0, y1) < P); ++y1) {}
          debug {
            writeln(z, " ", y0, " ", y1);
          }
          ans += z + 2 - y1;
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}