#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<string>
#include<cstring>
#include<map>
#include<functional>
#include<stack>
#include<list>
#include<set>
#include<deque>
#include<climits>
using namespace std;

typedef long long ll;

struct Movie
{
	int num, a, b;
	bool isUsed;
	Movie()
	{
		a = 0;
		b = 1e9;
		isUsed = false;
	}

	bool operator < (const Movie &a) const
	{
		if (isUsed != a.isUsed)
		{
			return isUsed;
		}
		return b > a.b;
	}
};

int main(){
	int N;
	Movie movie[100];
	cin >> N;
	for (int i = 0; i < N; i++)
	{
		cin >> movie[i].a >> movie[i].b;
		movie[i].num = i;
	}

	int ans = 0;
	for (int i = 1; i <= 31; i++)
	{
		Movie ma = Movie();
		ma.isUsed = true;
		for (int j = 0; j < N; j++)
		{
			if(i < movie[j].a || movie[j].b < i) continue;
			ma = max(ma, movie[j]);
		}
		movie[ma.num].isUsed = true;
		if (ma.isUsed) ans += 50;
		else ans += 100;
	}
	printf("%d\n", ans);
	return 0;
}