http://projecteuler.net/problem=15 [Answer:137846528820]

#include <iostream>

using namespace std;

int main()

{

    __int64 routes = 1;

    int n = 40;

    int m = 1;

    while ( n > m )

    {

        routes *= n;

        routes /= m;

        --n;

        ++m;

    }

    cout << routes << endl;

    return 0;

}