#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    int N;
    cin >> N;
    
    ll ans = 0;
    
    rep(days, 0, N) {
        string S, E;
        cin >> S >> E;
        
        int H, M, h, m;
        
        string tmp = "";
        
        int i = 0;
        while (true) {
            if (S[i] == ':') break;
            tmp += S[i];
            i++;
        }
        i++;
        H = stoi(tmp);
        tmp = "";
        
        rep(j, i, S.size()) tmp += S[j];
        M = stoi(tmp);
        
        tmp = "";
        
        i = 0;
        while (true) {
            if (E[i] == ':') break;
            tmp += E[i];
            i++;
        }
        i++;
        h = stoi(tmp);
        tmp = "";
        
        rep(j, i, E.size()) tmp += E[j];
        m = stoi(tmp);
        
        int s = H * 60 + M;
        int e = h * 60 + m;
        
        if (e - s >= 0) {
            ans += e - s;
            continue;
        }
        
        e += 24 * 60;
        ans += e - s;
    }
    
    cout << ans << '\n';
}