#include<stdio.h>

long power(int x,int y)
{
  int i;
  long result=x;;
  if (y==0) return 1;
  for(i=2;i<=y;i++)
    result*=x;
  return result;
}

int main()
{
  long n,m,y;
  long x;
  int flag=0;

  scanf("%ld %ld %ld",&n,&m,&y);
  for(x=0;x<m;x++)
  {
    if ( power(x,n) % m == y)
    {
      printf("%ld ",x);
      flag=1;
    }
  }
  if ( !flag )
    printf("-1");
  return 0;
}

Its giving wrong Test #4.

You think x^y fits in long when x is 100 and y is 100?
100^100...
You need (x^y) mod m (not x^y)!
Use this:

long power(int x,int y,int m)
{
int i;
long result=x;
if (y==0) return 1%m;
for(i=2;i<=y;i++)
result=(result*x)%m;
return result%m;
}

Thank you, I got accepted