#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;

    int ans = 0;


    rep(i,n){
        int a, b, c, d;
        string s;
        cin >> s;
        sscanf(s.c_str(), "%d:%d", &a, &b);
        cin >> s;
        sscanf(s.c_str(), "%d:%d", &c, &d);
        int tmp = c * 60 + d - (a * 60 + b);
        if(tmp < 0)tmp += 60 * 24;
        ans += tmp;
    }

    cout << ans << endl;
    return 0;
}