#include <iostream>
using namespace std;

int main(){
    int res = 0;
    int n,h1,m1,h2,m2;
    scanf("%d",&n);
    for(int i = 0; i < n; ++i){
        scanf("%d:%d %d:%d",&h1,&m1,&h2,&m2);
        if(h1<18){ h1+=24; }
        res+= (((24+h2)*60+m2)-(h1*60+m1));;
    }
    printf("%d\n",res);
    return 0;
}