#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    unsigned long long p,q,sol=0,st,dr,s=0,mij,i,n;
    fin>>n;
    q=50000000;
    st=1;
    dr=q;
    while(st<=dr)
    {s=0;
        mij=(st+dr)/2;p=1;
        for(i=1;i<=20;i++)
        {p=p*5;
            s=s+mij/p;

        }if(s==n){sol=mij;dr=mij-1;}
        else if(s<n)st=mij+1;

        else dr=mij-1;
    }if(sol==0)fout<<-1;
    else fout<<sol;
    return 0;
}