Loading..., Или так
#include <iostream>
int first_k_of_n(int n, int k)
{
if (k <= 0) return -1;
int temp = 0, res = 0, pow10 = 0;
n = abs(n);
while (n > 0)
{
temp = temp * 10 + n % 10;
n /= 10;
++pow10;
}
if (k > pow10) k = pow10;
for (int i = 0; i < k; ++i)
{
res = res * 10 + temp % 10;
temp /= 10;
}
return res;
}