#include<iostream.h>
#include<fstream.h>
int main ()
{
int p,n,pr,c,aux,i,ok;
ifstream b("fact.in");
b>>p;
b.close();
n=1;
ok=0;
while(ok!=1)
{
pr=1;c=0;
for(i=1;i<=n;i++)
{
pr=pr*i;
}
while(pr%10==0)
{
c++;
}
if(c==p)
{
aux=n;
ok=1;
}
n++;
}
ofstream v("fact.out");
v<<aux;
v.close();
return 0;
}