#ifdef ONLINE_JUDGE
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,mmx,avx,avx2")
#pragma GCC optimize("Ofast")
#endif
#include "bits/stdc++.h"
#ifndef ONLINE_JUDGE
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,mmx,avx")
#pragma GCC optimize("Ofast")
#endif
using namespace std;
typedef long long ll;
typedef long double ld;
#define PB push_back
#define MP make_pair
const int MOD=1000000007;
#define endl "\n"
#define fst first
#define snd second
const int UNDEF = -1;
const int INF=1<<30;
template<typename T> inline bool chkmax(T &aa, T bb) { return aa < bb ? aa = bb, true : false; }
template<typename T> inline bool chkmin(T &aa, T bb) { return aa > bb ? aa = bb, true : false; }
typedef pair<ll,ll> pll;typedef vector<ll> vll;typedef pair<int,int> pii;typedef vector<int> vi;typedef vector<vi> vvi;typedef vector<pii> vpii;typedef vector<pll> vpll;
template<typename T> void makeunique(vector<T> &vx) {sort(vx.begin(),vx.end());auto it=unique(vx.begin(),vx.end());vx.resize(std::distance(vx.begin(),it));}
#ifdef ONLINE_JUDGE
#define assert(...) /* nothing */
#endif
#define DEBUG_CAT
#ifdef DEBUG_CAT
#define dbg(...)   printf( __VA_ARGS__ )
#else 
#define dbg(...)   /****nothing****/
#endif
int rint();char rch();long long rlong();
// mt19937 rng; rng.seed(std::chrono::high_resolution_clock::now().time_since_epoch().count());
// template<typename T> int bins(vector<T> &v, T key) {int imin=0,imax=(int)v.size();while(imin<imax) {int imid=(imin+imax)>>1;if (v[imid]<key) imin=imid+1;else imax=imid;}return imin;}

int main() 
{
  ios_base::sync_with_stdio(false); cin.tie(0);
  ll n; cin>>n;
  vpll v(n);
  for (ll i=0;i<n;i++) {
    cin>>v[i].snd>>v[i].fst;
  }
  sort(v.begin(),v.end());
  ll r=n-1;
  ll b1=0,b2=0;
  for (ll i=0;i<n;i++) {
    ll discount=v[i].fst;
    while(r>=0&&b1+b2<discount) {
      ll take=min(v[r].snd,discount-(b1+b2));
      v[r].snd-=take;
      b2+=take;
      //printf("r:%lld take:%lld\n",r,take);
      if (v[r].snd==0) r--;
    }
    ll items=v[i].snd;
    //printf("i:%lld items:%lld\n",i,items);
    b1+=items;
    v[i].snd=0;
  }
  ll final=b1*1 + b2*2;
  printf("%lld\n",final);
}




static char stdinBuffer[1024];
static char* stdinDataEnd = stdinBuffer + sizeof (stdinBuffer);
static const char* stdinPos = stdinDataEnd;

void readAhead(size_t amount)
{
    size_t remaining = stdinDataEnd - stdinPos;
    if (remaining < amount) {
       memmove(stdinBuffer, stdinPos, remaining);
       size_t sz = fread(stdinBuffer + remaining, 1, sizeof (stdinBuffer) - remaining, stdin);
       stdinPos = stdinBuffer;
       stdinDataEnd = stdinBuffer + remaining + sz;
       if (stdinDataEnd != stdinBuffer + sizeof (stdinBuffer))
         *stdinDataEnd = 0;
    }
}

int rint()
{
    readAhead(16);

    int x = 0;
    bool neg = false;
    while(*stdinPos==' '||*stdinPos=='\n') ++stdinPos;
    if (*stdinPos == '-') {
       ++stdinPos;
       neg = true;
    }

    while (*stdinPos >= '0' && *stdinPos <= '9') {
       x *= 10;
       x += *stdinPos - '0';
       ++stdinPos;
    }

    return neg ? -x : x;
}
char rch()
{
    readAhead(16);
    while(*stdinPos==' '||*stdinPos=='\n') ++stdinPos;
    char ans=*stdinPos;
    ++stdinPos;
    return ans;
}
long long rlong()
{
    readAhead(32);

    long long x = 0;
    bool neg = false;
    while(*stdinPos==' '||*stdinPos=='\n') ++stdinPos;
    if (*stdinPos == '-') {
       ++stdinPos;
       neg = true;
    }

    while (*stdinPos >= '0' && *stdinPos <= '9') {
       x *= 10;
       x += *stdinPos - '0';
       ++stdinPos;
    }

    return neg ? -x : x;
}