#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>

using namespace std;



int main(){
    int n,sh,sm,eh,em,sum=0;
    
    scanf("%d",&n);
    
    for(int i=0;i<n;i++){
        scanf("%d:%d %d:%d",&sh,&sm,&eh,&em);
        
        sm+=sh*60;
        em+=eh*60;
        
        if(sm<em)
            sum+=em-sm;
        else
            sum+=em+24*60-sm;
    }
    
    printf("%d\n",sum);
    
    return 0;
}