#include <stdio.h>
#include <stdlib.h>

int main(void) {
  char input[12];
  int i, a, b, c, d, n, start, end, sum = 0;

  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%d:%d %d:%d", &a, &b, &c, &d);
    start = a * 60 + b;
    end = c * 60 + d;
    if (start > end) {
      sum += end + 24 * 60 - start;
    }
    else {
      sum += end - start;
    }
  }
  printf("%d\n", sum);

  return EXIT_SUCCESS;
}