#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int p;
    fin>>p;
    if(p==0) fout<<1;
    else
    {
        int st,dr,mij,sol,div5,puteri5;
        st=1;
        dr=p*5;
        sol=-1;
        while(st<=dr)
        {
            mij=(st+dr)/2;
            div5=5;
            puteri5=0;
            while(div5<=mij)
              {
                  puteri5=puteri5+mij/div5;
                  div5=div5*5;
              }
            if(puteri5>p) dr=mij-1;
            else if(puteri5<p) st=mij+1;
            else {
                   sol=mij;
                   dr=mij-1;
                 }
        }
        fout<<sol;
    }
    return 0;
}