#include<fstream>

using namespace std;
long long p,m;

int verifica(long long k)

{

int nr=0;

while(k)

{

nr=nr+k/5;

k=k/5;

}

return nr;

}

void caut(long long st,long long dr,long long x)

{

long gasit=0;

while(st<=dr&&!gasit)

{

m=(st+dr)/2;

if(verifica(m)==x)

gasit=1;

else

if(x>verifica(m))

st=m+1;

else

dr=m-1;


}

if(gasit==0)
m=-1;

}

int main()

{
ifstream f("fact.in");

ofstream g("fact.out");
f>>p;
caut(1,999999999,p);

if(m!=-1)
{

while(m)

{

if(verifica(m)==p)

m--;
else
break;
}
g<<m+1;

}

else
g<<m;
return 0;

}