#include <bits/stdc++.h>
#define nl '\n'
#ifdef LOCAL
#include "template/debug.hpp"
#else
#define dbg(...) ;
#define timer(...) ;
#endif
signed main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int n, m;
std::cin >> n >> m;
std::vector<int> P(n + m), C(n + m);
for (int i = 1; i < n + m; i++) {
std::cin >> P[i] >> C[i];
--P[i];
}
// we do dfs now
// f(x) is the minimum value to get
std::vector<int64_t> a(n + m), b(n + m);
std::vector<std::priority_queue<int64_t>> dp(n + m);
auto merge = [&](int i, int j) {
a[i] += a[j];
b[i] += b[j];
if (dp[i].size() < dp[j].size()) {
std::swap(dp[i], dp[j]);
}
while (dp[j].size()) {
dp[i].push(dp[j].top());
dp[j].pop();
}
};
for (int i = n + m - 1; i >= n; i--) {
a[i] = 1;
b[i] = -C[i];
dp[i].push(C[i]);
dp[i].push(C[i]);
merge(P[i], i);
}
dbg("done peasants");
auto pop_right = [&](int i) -> int64_t {
int64_t popped = dp[i].top();
int64_t v = a[i] * popped + b[i];
--a[i];
b[i] = v - a[i] * popped;
dp[i].pop();
return popped;
};
auto insert_right = [&](int i, int64_t p) -> void {
int64_t v = a[i] * p + b[i];
a[i]++;
b[i] = v - a[i] * p;
dp[i].push(p);
};
for (int i = n - 1; i > 0; i--) {
while (a[i] > 1) {
pop_right(i);
}
auto t1 = pop_right(i) + C[i];
auto t0 = pop_right(i) + C[i];
insert_right(i, t0);
insert_right(i, t1);
b[i] += C[i];
merge(P[i], i);
}
while (a[0] > 0) {
pop_right(0);
}
std::cout << a[0] * dp[0].top() + b[0] << nl;
}
