#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#define maxn 1000005
#define ll long long
using namespace std;
struct node
{
    ll to,next;
}g[maxn*2];
ll tot,head[maxn];
void addedge(ll u,ll v)
{
    g[tot].to=v;
    g[tot].next=head[u];
    head[u]=tot++;
}
ll n,ban[2],vis[maxn],val[maxn],f[2][maxn],bj,use,ans,p,num,E;
void dfs1(ll u,ll pre)
{
    //printf("%d\n",u);
    ll v,i;
    vis[u]=1;
    for(i=head[u];i!=-1;i=g[i].next)
    {
        v=g[i].to;
        if((i^1)==pre)
        continue;
        if(vis[v])
        {ban[0]=u;ban[1]=v;vis[v];E=i;continue;}
        dfs1(v,i);
    }
}
void dfs2(ll u,ll pre)
{
//	printf("%d %d %d\n",u,ban[use],ban[use^1]);
    //p++;
    //if(p>=4)
    //return ;
    ll v,i,ans1=0,ans0=0;
    for(i=head[u];i!=-1;i=g[i].next)
    {
        v=g[i].to;
        if((i^1)==pre)
        continue;
        if (i==E||(i^1)==E)
        continue;
        dfs2(v,i);
        ans1+=f[0][v];
        ans0+=max(f[0][v],f[1][v]);
    }
    f[0][u]=ans0;
    f[1][u]=ans1+val[u];
}

int main()
{
    ll i,x;
    scanf("%lld",&n);
    memset(head,-1,sizeof(head));
    for(i=1;i<=n;i++)
    {
        scanf("%lld%lld",&val[i],&x);
        addedge(i,x);
        addedge(x,i);
    }
    for(i=1;i<=n;i++)
    {
        if(!vis[i])
        {
        dfs1(i,-2);
    //	printf("%lld %lld\n",ban[0],ban[1]);
        use=0;
//		printf("%d %d\n",ban[0],ban[1]);
//		scanf("%d",&x);
        memset(f,0,sizeof(f[1]));
        dfs2(ban[1],-1);
        ans=f[0][ban[1]];
        use++;
        memset(f,0,sizeof(f[1]));
        dfs2(ban[0],-1);
        ans=max(ans,f[0][ban[0]]);
        num+=ans;
        //printf("%lld",ans);
        }
    }
    if(n==1)
    num=3;
    printf("%lld",num);
}