#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
    int recordtimes,sh,sm,wh,wm,total=0,ans=0;
    scanf("%d",&recordtimes);
    for(int i=0;i<recordtimes;i++)
    {
        scanf("%d:%d %d:%d",&sh,&sm,&wh,&wm);
        total=(wh*60+wm)-(sh*60+sm);
        if(total<0)
        {
            total+=60*24;
        }
        ans+=total;
    }
    printf("%d",ans);
}