using namespace std;
#include <bits/stdc++.h>
long long getPrefSum(int n) {
return 1LL * n * (n + 1) / 2;
}
int main() {
ios::sync_with_stdio(false);
cout.tie(nullptr), cin.tie(nullptr);
int n, m;
cin >> n >> m;
int k = min(m - 2, n - 1);
long long rows = getPrefSum(m - 2) - getPrefSum((m - 2) - k);
long long columns = getPrefSum(n - 1);
if (n >= m) columns -= getPrefSum((n - 1) - (k + 1));
else columns -= getPrefSum((n - 1) - k);
cout << columns + rows << endl;
return 0;
}
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