#include<stdio.h>
long long int x[300005], y[300005];
long long int dp[300005][2];
int main()
{
	long long int n;
	scanf("%lld", &n);
	long long int i;
	for (i = 0; i < n; i++)
		scanf("%lld %lld", &x[i], &y[i]);
	if (x[0] == y[0])
		dp[0][0] = dp[0][1] = x[0];
	else
		dp[0][0] = dp[0][1] = 0;
	long long int res1, res2;
	for (i = 1; i < n; i++)
	{
		res1 = dp[i - 1][0];
		if (y[i - 1] == x[i])
			res1 += x[i];
		res2 = dp[i - 1][1];
		if (x[i - 1] == x[i])
			res2 += x[i];
		if (res1 > res2)
			dp[i][0] = res1;
		else
			dp[i][0] = res2;
		res1 = dp[i - 1][0];
		if (y[i - 1] == y[i])
			res1 += y[i];
		res2 = dp[i - 1][1];
		if (x[i - 1] == y[i])
			res2 += y[i];
		if (res1 > res2)
			dp[i][1] = res1;
		else
			dp[i][1] = res2;
		if (x[i] == y[i])
		{
			dp[i][0] += x[i];
			dp[i][1] += x[i];
		}
	}
	res1 = dp[n - 1][0];
	if (res1 < dp[n - 1][1])
		res1 = dp[n - 1][1];
	printf("%lld\n", res1);
	return 0;
}