#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long p,a=1,z=400000000,e,az;
short ga;
long suma(long x)
{long i,s=0;
for(i=5;i<=x;i*=5)
s+=x/i;
return s;
}
int main()
{
f>>p;
if(p==1)
g<<0;
else
	if(p==0)
		g<<1;
	else
		{while(!ga&&a<=z)
			{az=(a+z)/2;
			 e=suma(az);
			 if(e<p)
				a=az+1; 
			 else
				 if(e>p)
					 z=az-1;
				 else
					 ga=1;
			}
		if(ga)
			{while(az%5)
				az--;
			g<<az;}
		else
			g<<-1;
	}
return 0;
}