#include<math.h>
#include<fstream.h>
ifstream fin("fact.in");
ofstream fout("fact.out");
long p,n,i,j,x;
int main()
{
	fin>>p;
	if(p)
	{
		n=5;
		do
		{
			n=n+5;
			i=0;
			x=0;
			do
			{
				i++;
			}
			while(pow(5,i)<=n);
			i--;
			for(j=1;j<=i;j++)
				x=x+n/(long)pow(5,i);
		}
		while(x<p);
		if(x>p)
			fout<<"-1";
		else
			fout<<n;
	}
	else
		fout<<"1";
	return 0;
}