a)
#include<iostream>
using namespace std;
int main() {
int n;
double p = 1;
cin >> n;
for (int i = 2; i <= 2 * n; i += 2)
p *= i;
cout << p;
return 0;
}
b)
#include<iostream>
using namespace std;
int main() {
int n, s = 0;
cin >> n;
for (int i = 1; i <= 3 * n - 2; i += 3)
s += i;
cout << s;
return 0;
}
c)
#include<iostream>
using namespace std;
int main() {
int n, s = 0;
cin >> n;
for (int i = 1; i <= 2*n-1; i +=2){
double p=1;
for(int j=1;j<=i;j+=2)
p*=j;
s+=p;
}
cout << s;
return 0;
}