#include <bits/stdc++.h>
using namespace std;
int main() {
    int N,H,M,h,m,an=0,D,d;
    cin>>N;
    while(N--){
        char c;
        cin>>H>>c>>M>>h>>c>>m;
        D=H*60+M;
        d=h*60+m;
        an+=d-D+(D>d)*(24*60);
    }
    cout<<an<<endl;
}