int ReplDigNinAwithB(int A, int N, int B)
{
    if (A<=0 || N<=0 || B<0 || B>9) return -1;
    int result=0, multiplier=1, currentPos=0;
    int temp=A;
    while (temp>0)
    {
        currentPos++;
        temp/=10;
    }
    if (N>currentPos) return -1;
    
    currentPos=0;
    while (A>0)
    {
        int digit=A%10;
        currentPos++;
        if (currentPos==N) digit=B;
        result = digit*multiplier + result;
        multiplier*=10;
        A/=10;
    }
    return result;
}