#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 + ;

const int M = 1e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 +;

int n, tot, a[N], fa[N], b[N], head[N];

bool vis[N];

LL f[N][];

struct Edge {

    int to, nx;

} edge[N << ];

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][] = , f[u][] = a[u];

    LL tmp[] = {};

    for(int i = head[u]; ~i; i = edge[i].nx) {

        int v = edge[i].to;

        if(v == fa || i == ban || (i ^ ) == ban) continue;

        dp(v, u, ban);

        tmp[] = f[u][], tmp[] = f[u][];

        tmp[] = max(tmp[], f[u][] + f[v][]);

        tmp[] = max(tmp[], f[u][] + f[v][]);

        tmp[] = max(tmp[], f[u][] + f[v][]);

        f[u][] = tmp[], f[u][] = tmp[];

    }

}

int main() {

    memset(head, -, sizeof(head));

    scanf("%d", &n);

    for(int i = ; i <= n; i++) {

        scanf("%d%d", &a[i], &b[i]);

        add(i, b[i]); add(b[i], i);

        fa[i] = i;

    }

    LL ans = ;

    for(int i = ; i <= n; i++) {

        int x = getRoot(i);

        int y = getRoot(b[i]);

        if(x != y) {

            fa[x] = y;

        } else {

            LL ret = ;

            dp(i, , i *  - );

            ret = max(ret, f[i][]);

            dp(b[i], , i *  - );

            ret = max(ret, f[b[i]][]);

            ans += ret;

        }

    }

    printf("%lld\n", ans);

    return ;

}

/*

*/