#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
typedef long long ll;
ll p,n;
ll nr(ll x)
{
    ll pw=1;
    ll rez=0;
    for(ll i=1;i<=19;i++)
    {
        pw=pw*5LL;
        ll q=x/pw;
        rez+=q;
    }
    return rez;
}
int main()
{
    fin>>p;
    n=1e18;
    ll st=1;
    ll dr=1e14;
    while(st<=dr)
    {
        ll mij=(st+dr)/2;
        if(nr(mij)>=p)
        {
            n=min(n,mij);
            dr=mij-1;
        }
        else
            st=mij+1;
    }
    if(nr(n)!=p)
        fout<<-1;
    else
        fout<<n;
    return 0;
}