#include <fstream>
#define nmax 500000000

using namespace std;

ifstream fin("factorial.in");
ofstream fout("factorial.out");

int p,hi,lo,x,mid,s;

int main()
{
    fin>>p;

    lo=0;
    hi=nmax;

    while (hi-lo>1)
    {
        mid = (hi+lo)/2;
        x=mid; s=0;
        while (x!=0)
        {
            s += x/5;
            x/=5;
        }
        if (p <= s) hi = mid;
        else lo = mid;
    }

    x=hi; s=0;
    while (x!=0)
    {
        s += x/5;
        x/=5;
    }

    if (p==s) fout<<hi;
    else fout<<-1;
 }