#include<bits/stdc++.h> #define LL long long #define fi first #define se second #define mk make_pair #define pii pair<int, int> #define y1 skldjfskldjg #define y2 skldfjsklejg using namespace std; const int N = 1e6 + 7; const int M = 1e5 + 7; const int inf = 0x3f3f3f3f; const LL INF = 0x3f3f3f3f3f3f3f3f; const int mod = 1e9 +7; int n, tot, a[N], fa[N], b[N], head[N]; bool vis[N]; LL f[N][2]; struct Edge { int to, nx; } edge[N << 1]; void add(int u, int v) { edge[tot].to = v; edge[tot].nx = head[u]; head[u] = tot++; } int getRoot(int x) { return fa[x] == x ? x : fa[x] = getRoot(fa[x]); } void dp(int u, int fa, int ban) { f[u][0] = 0, f[u][1] = a[u]; LL tmp[2] = {0}; for(int i = head[u]; ~i; i = edge[i].nx) { int v = edge[i].to; if(v == fa || i == ban || (i ^ 1) == ban) continue; dp(v, u, ban); tmp[0] = f[u][0], tmp[1] = f[u][1]; tmp[0] = max(tmp[0], f[u][0] + f[v][1]); tmp[0] = max(tmp[0], f[u][0] + f[v][0]); tmp[1] = max(tmp[1], f[u][1] + f[v][0]); f[u][0] = tmp[0], f[u][1] = tmp[1]; } } int main() { memset(head, -1, sizeof(head)); scanf("%d", &n); for(int i = 1; i <= n; i++) { scanf("%d%d", &a[i], &b[i]); add(i, b[i]); add(b[i], i); fa[i] = i; } LL ans = 0; for(int i = 1; i <= n; i++) { int x = getRoot(i); int y = getRoot(b[i]); if(x != y) { fa[x] = y; } else { LL ret = 0; dp(i, 0, i * 2 - 2); ret = max(ret, f[i][0]); dp(b[i], 0, i * 2 - 2); ret = max(ret, f[b[i]][0]); ans += ret; } } printf("%lld\n", ans); return 0; } /* */