#include<bits/stdc++.h>
using namespace std;
using Int = signed;
//INSERT ABOVE HERE
signed main(){
  Int n;
  scanf("%d\n",&n);
  Int ans=0;
  for(Int i=0;i<n;i++){
    Int a,b,c,d;
    scanf("%d:%d %d:%d\n",&a,&b,&c,&d);
    Int x=24*60;
    x-=a*60+b;    
    x+=c*60+d;
    ans+=x%(24*60);
  }
  cout<<ans<<endl;
  return 0;
}