package contest1910; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.ArrayList; import java.util.Arrays; import java.util.InputMismatchException; import java.util.List; public class B { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int n = ni(); int[] a = new int[n-1]; int[] b = new int[n-1]; for(int i = 0;i < n-1;i++) { a[i] = ni(); b[i] = ni(); } List es = new ArrayList<>(); int src = 2*(n-1), sink = src + 1; long lsum = 0, rsum = 0; for(int i = 0;i < n-1;i++) { lsum += a[i]; rsum += b[i]; es.add(new Edge(src, i, a[i])); es.add(new Edge(i+n-1, sink, b[i])); } for(int i = 0;i < n-1;i++) { for(int j = 0;j < n-1;j++) { if(i != j) { es.add(new Edge(i, j+n-1, 99999)); } } } long F = maximumFlowDinicNoRec(compileWD(sink+1, es), src, sink); out.println(F + 1); } public static class Edge { public int from, to; public long capacity; public long flow; public Edge complement; public boolean cloned; public Edge(int from, int to, long capacity) { this.from = from; this.to = to; this.capacity = capacity; } } public static void reset(Edge[][] g) { for(Edge[] row : g){ for(Edge e : row){ e.flow = e.cloned ? e.capacity : 0; } } } public static Edge[][] compileWD(int n, List edges) { Edge[][] g = new Edge[n][]; // cloning for(int i = edges.size()-1;i >= 0;i--){ Edge origin = edges.get(i); Edge clone = new Edge(origin.to, origin.from, origin.capacity); clone.flow = origin.capacity; clone.complement = origin; clone.cloned = true; origin.complement = clone; edges.add(clone); } int[] p = new int[n]; for(Edge e : edges)p[e.from]++; for(int i = 0;i < n;i++)g[i] = new Edge[p[i]]; for(Edge e : edges)g[e.from][--p[e.from]] = e; return g; } public static Edge[][] compileWU(int n, List edges) { Edge[][] g = new Edge[n][]; // cloning for(int i = edges.size()-1;i >= 0;i--){ Edge origin = edges.get(i); Edge clone = new Edge(origin.to, origin.from, origin.capacity*2); origin.flow = origin.capacity; clone.flow = origin.capacity; clone.complement = origin; clone.cloned = true; origin.complement = clone; origin.capacity *= 2; edges.add(clone); } int[] p = new int[n]; for(Edge e : edges)p[e.from]++; for(int i = 0;i < n;i++)g[i] = new Edge[p[i]]; for(Edge e : edges)g[e.from][--p[e.from]] = e; return g; } public static long maximumFlowDinic(Edge[][] g, int source, int sink) { int n = g.length; int[] d = new int[n]; int[] q = new int[n]; long ret = 0; while(true){ Arrays.fill(d, -1); q[0] = source; int r = 1; d[source] = 0; for(int v = 0;v < r;v++){ int cur = q[v]; for(Edge ne : g[cur]){ if(d[ne.to] == -1 && ne.capacity - ne.flow > 0) { q[r++] = ne.to; d[ne.to] = d[cur] + 1; } } } if(d[sink] == -1)break; int[] sp = new int[n]; for(int i = 0;i < n;i++)sp[i] = g[i].length - 1; ret += dfsDinic(d, g, sp, source, sink, Long.MAX_VALUE); } return ret; } private static long dfsDinic(int[] d, Edge[][] g, int[] sp, int cur, int sink, long min) { if(cur == sink)return min; long left = min; for(int i = sp[cur];i >= 0;i--){ Edge ne = g[cur][i]; if(d[ne.to] == d[cur]+1 && ne.capacity - ne.flow > 0){ long fl = dfsDinic(d, g, sp, ne.to, sink, Math.min(left, ne.capacity - ne.flow)); if(fl > 0){ left -= fl; ne.flow += fl; ne.complement.flow -= fl; if(left == 0){ sp[cur] = i; return min; } } } } sp[cur] = -1; return min-left; } public static long maximumFlowDinicNoRec(Edge[][] g, int source, int sink) { int n = g.length; int[] d = new int[n]; // distance int[] q = new int[n]; // queue for BFS long ret = 0; int[] stack = new int[n]; long[] lefts = new long[n]; // left to flow long[] parflow = new long[n]; int[] probe = new int[n]; // search pointer while(true){ // BFS Arrays.fill(d, -1); q[0] = source; int r = 1; d[source] = 0; for(int v = 0;v < r;v++){ int cur = q[v]; for(Edge ne : g[cur]){ if(d[ne.to] == -1 && ne.capacity - ne.flow > 0) { q[r++] = ne.to; d[ne.to] = d[cur] + 1; } } } if(d[sink] == -1)break; // DFS for(int i = 0;i < n;i++)probe[i] = g[i].length-1; int sp = 0; stack[sp] = source; lefts[sp] = Long.MAX_VALUE / 10; parflow[sp] = 0; sp++; long delta = 0; boolean down = true; while(sp > 0){ int cur = stack[sp-1]; long left = lefts[sp-1]; if(cur == sink){ delta += left; parflow[sp-1] = left; sp--; down = false; continue; } if(!down){ if(parflow[sp] > 0){ lefts[sp-1] -= parflow[sp]; left = lefts[sp-1]; Edge ne = g[cur][probe[cur]]; ne.flow += parflow[sp]; ne.complement.flow -= parflow[sp]; parflow[sp-1] += parflow[sp]; } if(left > 0)probe[cur]--; } if(left > 0 && probe[cur] >= 0){ down = true; Edge ne = g[cur][probe[cur]]; if(d[ne.to] == d[cur]+1 && ne.capacity - ne.flow > 0){ lefts[sp] = Math.min(left, ne.capacity - ne.flow); stack[sp] = ne.to; parflow[sp] = 0; sp++; }else{ probe[cur]--; } }else{ down = false; sp--; } } ret += delta; } return ret; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){ // @Override // public void run() { // long s = System.currentTimeMillis(); // solve(); // out.flush(); // if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // } // }; // t.start(); // t.join(); } public static void main(String[] args) throws Exception { new B().run(); } private byte[] inbuf = new byte[1024]; public int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private long[] nal(int n) { long[] a = new long[n]; for(int i = 0;i < n;i++)a[i] = nl(); return a; } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[][] nmi(int n, int m) { int[][] map = new int[n][]; for(int i = 0;i < n;i++)map[i] = na(m); return map; } private int ni() { return (int)nl(); } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }