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- #include<bits/stdc++.h>
- using namespace std;
- using ll = long long;
- ll Cnr(int n, int r) {
- ll s = 1;
- if (r * 2 > n) {
- r = n - r;
- }
- for (int i = 0; i < r; i++) {
- s *= (n - i);
- }
- for (int i = r; i >= 2; i--) {
- s /= i;
- }
- return s;
- }
- int main() {
- int n, r;
- while (cin >> n >> r) {
- cout << Cnr(n, r) << endl;
- }
- return 0;
- }
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