#include <bits/stdc++.h>
using namespace std;

signed main(){
    int ans=0;
    int n;cin>>n;
    while(n--){
        int H,M,h,m;char c;
        cin>>H>>c>>M>>h>>c>>m;
        if(H>h)h+=24;
        ans+=h*60+m-H*60-M;
    }
    cout<<ans<<endl;
}