#include <stdio.h>

long nr(long n)
{
long n2,n5,i;

for (n2=0,i=2;i<=n;i*=2)
n2+=(n/i);

for (n5=0,i=5;i<=4000000000;i*=5)
n5+=(n/i);

if (n2<n5) return n2;
return n5;
}

int main()
{
long ls,ld,p,n,s;
freopen("fact.in","rt",stdin);
freopen("fact.out","wt",stdout);
scanf("%ld",&p);

ls=s=1;
ld=999999999;
while (ls<=ld)
{
n=(ls+ld)/2;
if (nr(n)>=p)
    {
    s=n;
    ld=n-1;
    }
  else
    ls=n+1;
    }
if (nr(s)!=p) printf("-1");
else printf("%ld",s);
return 0;}