UVA 11401 Triangle Counting

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You are given n rods of length 1, 2…, n. You have to pick any 3 of them & build a triangle. How many distinct triangles can you make? Note that, two triangles will be considered different if they have at least 1 pair of arms with different length.

 

Input

 

The input for each case will have only a single positive integer n (3<=n<=1000000). The end of input will be indicated by a case with n<3. This case should not be processed.

 

Output

 

For each test case, print the number of distinct triangles you can make.

 

Sample Input                                                  Output for Sample Input

5 8 0

3 22

 

#include<iostream>
#include<algorithm>
using namespace std;
unsigned long long f[1000010],i,n;
int main()
{f[3]=0;for(i=4;i<=1000000;i++)f[i]=f[i-1]+((i-1)*(i-2)/2-(i-1)/2)/2;while(cin>>n&&n>=3){cout<<f[n]<<endl;}
return 0;
}

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