//{{{
#include <bits/stdc++.h>
using namespace std;
#define rep(...) repN((__VA_ARGS__,rep3,rep2,loop,~))(__VA_ARGS__)
#define loop(n) rep2(_loop_,n)
#define rep2(i,n) rep3(i,0,n)
#define rep3(i,begin,end) for(int i=(int)(begin),i##_end=(int)(end);i<i##_end;++i)
#define repN(a) repX a
#define repX(a0,a1,a2,x,...) x
typedef long long ll;
const int MOD = 1e9+7;
//}}}

int main(){
	int N;
	cin >> N;
	int ans = 0;
	rep(i, N){
		int H, M;
		int h, m;
		scanf("%d:%d", &H, &M);
		scanf("%d:%d", &h, &m);
		int a = H * 60 + M;
		int b = h * 60 + m;
		if(b < a) b += 24 * 60;
		ans += b - a;
	}
	printf("%d\n", ans);
	return 0;
}