#include <cstdio>
int main(){
    int N,min=0,H,M,h,m;
    scanf("%d",&N);
    for(int i=0;i<N;i++){
        scanf("%d:%d %d:%d",&H,&M,&h,&m);
        min+=(h*60+m)-(H*60+M);
        if(H*60+M>h*60+m)min+=24*60;
    }
    printf("%d\n",min);
    return 0;
}