#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define fi first
#define in inline
#define se second
#define mp make_pair
#define pb push_back
const int N = 1e5+10;

ll read(){
	ll x = 0,f = 1;char c = getchar();
	for(;c < '0' || c > '9';c = getchar())if(c == '-')f = -1;
	for(;c >= '0' && c <= '9';c = getchar())x = (x<<1) + (x<<3) + c-'0';
	return x * f;
}


int n;
ll t[N],a[N],f[N];



int main(){
	freopen("a.in","r",stdin);
	freopen("a.out","w",stdout);
	n = read();
	for(int i = 1;i <= n;i++)t[i] = read(),a[i] = read();
	memset(f,0x3f,sizeof f);
	f[0] = 0;
	for(int i = 1;i <= n;i++){
		ll mx = a[i];
		for(int j = i-1;j >= 0;j--){
			int k = max(t[i],f[j]);
			f[i] = min(f[i],k + 2 * mx);
			mx = max(mx,a[j]);
		}
//		printf("%lld ",f[i]);
	}
//	printf("\n---\n");
	printf("%lld\n",f[n]);


	return 0;

}