#include <iostream>
#include <string>
using namespace std;
int main()
{
    int n,h1,m1,h2,m2,count=0;
    char c1,c2;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>h1>>c1>>m1>>h2>>c2>>m2;
        while(h2!=h1||m1!=m2){
            m2--;
            if(m2<0){
                h2--;
                m2=59;
                if(h2<0)h2=23;
            }
            count++;
        }
    }
    cout<<count<<endl;
    return 0;
}