#include<stdio.h>

int main(void){
  int i;
  int N, H, M, h, m;
  int t;
  scanf("%d", &N);
  for(i = 0; i < N; i++){
    scanf("%d:%d %d:%d", &H, &M, &h, &m);
    if(H * 60 + M > h * 60 + m) t += (24 - H) * 60 - M;
    else t -= H * 60 + M;
    t += h * 60 + m;
  }
  printf("%d\n", t);
  return 0;
}