#include<fstream>
#include<climits>
using namespace std;
int multiplicitate(int x)
{
    int p=5,s=0;
    while(x/p)
    {
        s+=x/p;
        p*=5;
    }
    return s;
}
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int st,dr,mij=0,p; bool ok=0;
    f>>p;
    st=1,dr=INT_MAX-1;
    while(st<=dr&&!ok)
    {
        mij=(st+dr)/2;
        if(multiplicitate(mij)==p)
        {
             while(multiplicitate(mij)==p&&mij>0) mij--;ok=1;
        }
        else
        {
            if(multiplicitate(mij)<p) st=mij+1;
            else dr=mij-1;
        }
    }

    if(ok) g<<(mij+1)<<'\n';
    else g<<-1<<'\n';
    g.close();
    return 0;
}