My code:

#include <iostream>
using namespace std;

double fac(int n)
{
    double l = 1.0;
    for(int i = 1; i <= n; i++)
        l *=i;
    return l;
}
double A(int m, int n)
{
    return fac(m)/fac(m-n);
}

void main()
{
    int n;
    double soni = 0;
    cin >> n;

    for(int i = 2; i<=n; i++)
    {
        soni += A(n,i);
    }

    cout.precision(0);
    cout << fixed << soni;
}

WA#13
Where is my mistake? pls help me

i have met the same problem with u

Precision

Edited by author 28.01.2012 00:07

Edited by author 28.01.2012 00:07

Use C# & BigInteger & permutaions
http://ru.wikipedia.org/wiki/Размещение

primer
21=138879579704209680000
19=330665665962403980
20=6613313319248079980

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21-138879579704209680000