// 想定解
#include <bits/stdc++.h>
using namespace std;
void rc(int v,int mn,int mx){if(v<mn||mx<v){cerr<<"error"<<endl;exit(1);}}
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

const int MAXN = 30;

int main(){
    int N;
    cin >> N; rc(N, 1, MAXN);
    int result = 0;
    REP(i,N){
        int h1,m1,h2,m2; char d;
        cin >> h1 >> d >> m1 >> h2 >> d >> m2;
        rc(h1,0,23); rc(m1,0,59); rc(h2,0,23); rc(m2,0,59);
        result += ((24+h2-h1)*60+m2-m1)%(24*60);
    }
    cout << result << endl;
    return 0;
}