模拟

// Brute Force 
// Time Complexity: O(n * M * N)
#include <iostream>
#include <cstring>

using namespace std;

const int N = 105;
int g[N][N], n, x1, y1, x2, y2;

int main(void) {
  scanf("%d", &n);
  while (n--) {
    scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
    for (int y = N - 1 - y2; y < N - 1 - y1; ++y)
      for (int x = x1; x < x2; ++x) g[y][x] = 1;
  }

  int ans = 0;  
  for (int y = 0; y < N; ++y)
    for (int x = 0; x < N; ++x)
      ans += g[y][x];

  printf("%d\n", ans);
  return 0;
}