#include <bits/stdc++.h>

#define ll long long
#define ld long double
#define rep(i,a,b) for (int i = a; i < b; i++)
#define irep(i,a,b) for (int i = a; i > b; i--)
#define print(n) cout << n << endl
#define rup(a,b) (a+b-1)/b

using namespace std;
int calc(string a,string b){
    int now = 0;
    int ha,sa;
    bool p = false;
    rep(i,0,a.size()){
        if (a[i]==':'){
            p = true;
            ha = now;
            now = 0;
            continue;
        }
        now *= 10;
        now += int(a[i]-'0');
    }
    sa = now;
    int hb,sb;
    now = 0;
    rep(i,0,b.size()){
        if(b[i]==':'){
            hb = now;
            now = 0;
            continue;
        }
        now *= 10;
        now += int(b[i]-'0');
    }
    sb = now;
    int count;
    count = hb - ha;
    if (count < 0) count += 24;
    count *= 60;
    count += sb - sa;
    return count;

}
int main(){
    cout << fixed << setprecision(15);
    
    int n;
    cin >> n;
    int count = 0;
    rep(i,0,n){
        string a,b;
        cin>>a>>b;
        count += calc(a,b);

    }
    print(count);
    
    //system("pause");
    return 0;
}