#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>

#define ALL(x) (x).begin(),(x).end()

using namespace std;
int main(){
    int n,ans = 0;
    cin >> n;
    for(int i = 0;i < n;i++){
        int H,M,h,m;
        scanf("%d:%d",&H,&M);
        H = H*60+M;
        scanf("%d:%d",&h,&m);
        h = h*60+m;
        if(h > H)ans += h - H;
        else ans += 1440 - H + h;
    }
    cout << ans << endl;
    return 0;
}