#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
int p,nr5,n,x,k,y;
int main()
{
f>>p;
n=0;
nr5=0;
y=0;
while(nr5<p)
{
n=n+5;
y++;
x=y;
k=1;
while(x%5==0)
{
k++;
x=x/5;
}
nr5=nr5+k;
}
if(p==0)
g<<"1";
else
if(nr5==p)
g<<n;
else
g<<"-1";
g<<'\n';
f.close();
g.close();
return 0;
}