401.cpp

#include <cstdio>

long long C (int n, int k) {
    if (n-k < k) {
        return C(n, n-k);
    }

    long long answer = 1;
    for (int i = 1; i <= k; ++i) {
        answer *= (n-k+i);
        answer /= i;
    }

    return answer;
}

int main() {
    int n, a, b;
    scanf("%d %d %d", &n, &a, &b);

    auto answer = (__float128) C(n+a, a) * (__float128) C(n+b, b);

    long long high = answer / 1e17;
    long long low = answer - high * (__float128)1e17;

    if (high != 0) {
        printf("%lld%017lld", high, low);
    } else {
        printf("%lld", low);
    }

    return 0;
}