#include <iostream>
#include <fstream>
using namespace std;
typedef long long ll;
ifstream f("fact.in");
ofstream g("fact.out");

ll p;
ll zero(ll n)
{
    ll rez = 0;
    ll s=5;
    while(n/s)
    {
        rez+=n/s;
        s*=5;
    }
    return rez;
}
ll rasp()
{
    ll i,j,m;
    ll z;
    i=1;
    j=400000020;
    bool ok = false;
    while(i<j)
    {
        m=(i+j)/2;
        z=zero(m);
        if(z<p)
            i=m+1;
        else if(z > p)
            j=m-1;
        else
        {
            j=m;
            ok=true;
        }
    }
    if(ok)  return i;
    else    return -1;
}
int main()
{
    f>>p;
    g<<rasp();
    f.close();
    g.close();
    return 0;
}