#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=9;
		do
		{
			n++;
			x=0;
			for(i=5;i<=n;i=i+5)
			{
				ci=i;
				while(ci%5==0)
				{
					x=x+ci/5;
					ci=ci/5;
				}
			}	
		}
		while(x<p);
		if(x>p)
			fout<<"-1";
		else
			fout<<n;
	}
	else
		fout<<"1";
	return 0;
}