#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; i++) //[0,n)
#define srep(i,a,b) for(int i = a; i < b; i++) //[a,b)
#define all(A) (A).begin(),(A).end()
#define rall(A) (A).rbegin(),(A).rend()
#define pmt(A) next_permutation(A)
using namespace std;
using ll = long long;
using ull = unsigned long long;
using P = pair<ll,ll>;
using pq = priority_queue<ll,vector<ll>,greater<ll>>;
const ll inf = 8e18;
const int iinf = (int)1e9;
const int mod9 = 998244353;
const int mod1 = 1000000007;
struct Edge { int to; ll cost; int from; };
bool compe(const Edge &e,const Edge &e2){ return e.cost < e2.cost; }
using Graph = vector<vector<int>>;
using EGraph = vector<Edge>;
using SGraph = vector<set<ll>>;
template <typename T>
int siz(T& a){ return (int)a.size(); }
ll squa(ll a){ return a*a; }
int ceil(int a,int b){ return (a+b-1)/b; }
using namespace std;

vector<string> split(string s,char c){
    vector<string> res;
    rep(i,siz(s)){
        string v = "";
        while(i < siz(s) && s[i] != c) v += s[i++];
        res.push_back(v);
    }
    return res;
}

int main(){
    int n; cin >> n;
    ll ans = 0;
    rep(_,n){
        string s,t; cin >> s >> t;
        auto sp = split(s,':');
        auto tp = split(t,':');
        
        int h = stoi(sp[0]),m = stoi(sp[1]);
        int h2 = stoi(tp[0]),m2 = stoi(tp[1]);

        if(h > h2) h2 += 24;
        ans += (h2*60+m2)-(h*60+m);
    }
    cout << ans;
}