#include <iostream>
#define llint long long
#define inf 1e18

using namespace std;

llint n;
llint c[100005], d[100005];
llint dp[100005][2];

int main(void)
{
	cin >> n;
	for(int i = 1; i <= n; i++) cin >> c[i] >> d[i];
	
	for(int i = 1; i <= n; i++) dp[i][0] = dp[i][1] = inf;
	dp[1][0] = c[1], dp[1][1] = 2*c[1];
	for(int i = 1; i < n; i++){
		dp[i+1][0] = min(dp[i+1][0], dp[i][0] + c[i+1]+d[i+1]);
		dp[i+1][1] = min(dp[i+1][1], dp[i][0] + c[i+1]+d[i+1]+c[i+1]);
		dp[i+1][0] = min(dp[i+1][0], dp[i][1] + c[i+1]);
		dp[i+1][1] = min(dp[i+1][1], dp[i][1] + c[i+1]+d[i+1]);
		dp[i+1][1] = min(dp[i+1][1], dp[i][1] + c[i+1]+c[i+1]);
		
	}
	cout << dp[n][1] << endl;
	
	return 0;
}