#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream h("fact.out");
long long b=1000000000;
long long p;

long long r(long c )
{
     long long p=0;
     while(c)
     {
        p += c/5;
        c /= 5;
     }
     return p;
}
void caut(long long a, long long b)
{long long m;
if(p==0) h<<1;
else{
    while (a <= b) {
        m = (a + b) / 2;
        if (r(m) <= p)
            a = m + 1;
        else
            b = m - 1;
    }
    m = (a + b) / 2;
    int ok=0;
    while(r(m) == p)
    {
        m --;
        ok=1;}
   if(ok)
       h<<++m;
   else h<<-1;
            }
}
int main()
{
    f>>p;
    caut(0,b);
    return 0;
}