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#include <bits/stdc++.h>
//https://www.luogu.com.cn/blog/x4Cx58x54/solution-p2638
//经典题
using namespace std;
typedef unsigned long long ULL;
int n, a, B;
ULL ans;
//求组合数的优化后办法
//优点：从1开始除和乘，可以防止过早溢出和除法除不尽
ULL C(int n, int m) {
ULL sum = 1;
for (int i = 1; i <= m; i++)
sum = sum * (n - m + i) / i;
return sum;
}
int main() {
cin >> n >> a >> b;
for (int i = 0; i <= a; i++)
for (int j = 0; j <= b; j++)
ans += C(n + i - 1, n - 1) * C(n + j - 1, n - 1);
cout << ans << endl;
return 0;
