#include<bits/stdc++.h>
#define fi first
#define se second
#define eb emplace_back
#define mp make_pair
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128; 
template<typename T,typename U>
T ceil(T x, U y) {return (x>0?(x+y-1)/y:x/y);}
template<typename T,typename U>
T floor(T x, U y) {return (x>0?x/y:(x-y+1)/y);}
template<class T,class S>
bool chmax(T &a,const S b) {return (a<b?a=b,1:0);}
template<class T,class S>
bool chmin(T &a,const S b) {return (a>b?a=b,1:0);}
int popcnt(int x) {return __builtin_popcount(x);}
int popcnt(ll x)  {return __builtin_popcountll(x);}
int topbit(int x) {return (x==0?-1:31-__builtin_clz(x));}
int topbit(ll x)  {return (x==0?-1:63-__builtin_clzll(x));}
int lowbit(int x) {return (x==0?-1:__builtin_ctz(x));}
int lowbit(ll x)  {return (x==0?-1:__builtin_ctzll(x));}

#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
typedef pair<int,int> pii; 
typedef vector<int> vi;
typedef vector<pii> vp;
typedef tuple<int,int,int> tiii;
int read() {
  int x=0,w=1; char c=getchar(); 
  while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
  while(isdigit(c)) {x=x*10+(c-'0'); c=getchar();}
  return x*w;
}

const int N=1005,M=20005,inf=0x3f3f3f3f;
int n,f[N][M],a[N],b[N],m;

signed main() {
  n=read()-1, b[0]=read(), m=b[0];
  rep(i,1,n) a[i]=read(), b[i]=read();
  rep(i,1,n) chmax(m,a[i]+b[i]);
  rep(i,0,b[0]-1) f[0][i]=i;
  rep(i,b[0],m) f[0][i]=-inf;
  rep(i,1,n) {
    int w=0;
    rep(j,0,a[i]-1) chmax(w,f[i-1][j]);
    rep(j,0,b[i]-1) chmax(f[i][j],w+j);
    rep(j,0,m) {
      if(a[i]+b[i]<=j) chmax(f[i][j],f[i-1][j]);
      else {
        if(j>=a[i]) chmax(f[i][j-a[i]],f[i-1][j]);
        else chmax(f[i][j+b[i]],f[i-1][j]+b[i]);
      }
    }
  }
  int ans=0;
  rep(j,0,m) chmax(ans,f[n][j]);
  printf("%d\n",ans);
  return 0;
}