#include<bits/stdc++.h>
using namespace std;

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)

#define ll long long
#define ull unsigned ll

void reader(int *x){int k,m=0;*x=0;for(;;){mygc(k);if(k=='-'){m=1;break;}if('0'<=k&&k<='9'){*x=k-'0';break;}}for(;;){mygc(k);if(k<'0'||k>'9')break;*x=(*x)*10+k-'0';}if(m)(*x)=-(*x);}
void reader(int *x, int *y){reader(x);reader(y);}

void* setDirectEdge(int N, int M, int A[], int B[], int **es, int ***edge, void *workMemory){int i;*es=(int*)workMemory;*edge=(int**)((*es)+N);(*edge)[0]=(int*)((*edge)+N);rep(i,N)(*es)[i]=0;rep(i,M)(*es)[A[i]]++;REP(i,1,N)(*edge)[i]=(*edge)[i-1]+(*es)[i-1];workMemory=(void*)((*edge)[N-1]+(*es)[N-1]);rep(i,N)(*es)[i]=0;rep(i,M)(*edge)[A[i]][(*es)[A[i]]++]=B[i];return workMemory;}
void* getReverseGraph(int N, int *es, int **edge, int **r_es, int ***r_edge, void *workMemory){int i,j,k;*r_es=(int*)workMemory;*r_edge=(int**)((*r_es)+N);(*r_edge)[0]=(int*)((*r_edge)+N);rep(i,N)(*r_es)[i] = 0;rep(i,N)rep(j,es[i])(*r_es)[edge[i][j]]++;REP(i,1,N)(*r_edge)[i]=(*r_edge)[i-1]+(*r_es)[i-1];workMemory=(void*)((*r_edge)[N-1]+(*r_es)[N-1]);rep(i,N)(*r_es)[i]=0;rep(i,N)rep(j,es[i])k=edge[i][j],(*r_edge)[k][(*r_es)[k]++]=i;return workMemory;}

int StronglyConnectedComponentsDFS(int *es, int **edge, int num[], int st, int mx){int i,j;num[st]=-2;rep(i,es[st]){j=edge[st][i];if(num[j]==-1)mx=StronglyConnectedComponentsDFS(es,edge,num,j,mx);}num[st]=mx;return mx+1;}
int StronglyConnectedComponents(int N, int *es, int **edge, int res[], void *workMemory){int i,j,k,t=0,*s,**e,*q,z,*n,*r;workMemory=getReverseGraph(N,es,edge,&s,&e,workMemory);q=(int*)workMemory;n=q+N;r=n+N;rep(i,N)res[i]=n[i]=-1;k=0;rep(i,N)if(n[i]==-1)k=StronglyConnectedComponentsDFS(es,edge,n,i,k);rep(i,N)r[n[i]]=i;for(k=N-1;k>=0;k--){i=r[k];if(res[i]>=0)continue;res[i]=t;z=0;q[z++]=i;while(z){i=q[--z];rep(j,s[i])if(res[e[i][j]]==-1)res[e[i][j]]=t,q[z++]=e[i][j];}t++;}return t;}

int N;
int A[222], B[222], L[222];
int com[222], deg[222], mn[222];

int main(){
  int i, j, k, nn;
  int res;
  int *es, **edge;
  void *mem = malloc(10000000);

  reader(&N);
  rep(i,N) reader(L+i,A+i), A[i]--, B[i]=i;
  mem = setDirectEdge(N, N, A, B, &es, &edge, mem);

  nn = StronglyConnectedComponents(N, es, edge, com, mem);

  res = 0;
  rep(i,N) res += L[i];
  rep(i,N) if(com[A[i]] != com[B[i]]) deg[com[B[i]]]++;

  rep(i,nn) mn[i] = 10000;
  rep(i,N) mn[com[i]] = min(mn[com[i]], L[i]);

  rep(i,nn) if(!deg[i]) res += mn[i];

  printf("%.1f\n",res/2.0);

  return 0;
}