#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 300005
#define ff first
#define ss second
int n, m;
vector<pair<int, ll> > child[N];
pair<ll, ll> bound[N];
ll get(int v, ll val){
ll res = 0;
for(auto x : child[v]){
if(val <= bound[x.ff].ff) res += bound[x.ff].ff - val;
else if(val >= bound[x.ff].ss) res += val - bound[x.ff].ss;
else res += val;
}
return res;
}
ll dfs(int v){
if(v > n){
bound[v] = {0, 0};
return 0;
}
ll res = 0;
ll lll = LLONG_MAX, rrr = 0, m, l, r, L, R;
for(auto x : child[v]){
res += dfs(x.ff);
bound[x.ff].ff += x.ss;
bound[x.ff].ss += x.ss;
lll = min(lll, bound[x.ff].ff);
rrr = max(rrr, bound[x.ff].ss);
}
l = lll;
r = rrr;
while(l != r){
m = (l + r) >> 1;
if(get(v, m) < get(v, m + 1)) r = m;
else l = m + 1;
}
L = l;
R = l;
while(lll != L){
m = (lll + L) >> 1;
if(get(v, m) == get(v, L)) L = m;
else lll = m + 1;
}
while(rrr != R){
m = (rrr + R + 1) >> 1;
if(get(v, m) == get(v, R)) R = m;
else rrr = m - 1;
}
bound[v].ff = L;
bound[v].ss = R;
res += get(v, L);
// cout<<v<<' '<<L<<' '<<R<<' '<<res<<'\n';
return res;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin>>n>>m;
for(int i = 2; i <= n + m; i++){
int p;
ll c;
cin>>p>>c;
child[p].push_back({i, c});
}
cout<<dfs(1);
}
