#include <fstream>
using namespace std;
ifstream fi("fact.in");
ofstream fo("fact.out");
int p,st,dr,m;

int verificare(int nr)
{
    int c=0;
    int x=5;
    while(nr/x>0)
    {
        c=c+nr/x;
        x=x*5;
    }
    return c;
}

int main()
{
    fi>>p;
    st=1;
    dr=p*5;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(verificare(m)<p)
            st=m+1;
        else
            dr=m-1;
    }
    if(verificare(st)==p)
        fo<<st;
    else
        fo<<-1;
    fi.close();
    fo.close();
    return 0;
}