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

inline int rd() {
    int x = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar());
    for (; isdigit(c); c = getchar()) x= x * 10 + (c ^ 48);
    return x;
}

ll ans = 0;

struct vec {
    ll x, y;
    inline ll operator * (vec &b) {
        return x * b.y - y * b.x;
    }
}c[100];

inline void work() {
    int n = rd();
    ll nw = 0;
    for (int i = 1; i <= n; ++i) {
        c[i].x = rd(); c[i].y = rd();
    }
    for (int i = 1; i <= n; ++i) {
        int j = i + 1 > n ? 1 : i + 1;
        nw += c[i] * c[j];
    }
    ans += abs(nw);
}

int main() {
    int t = rd();
    while (t--) work();
    printf("%lld\n", ans / 2);
    return 0;
}