#include <fstream>

using namespace std;

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

long long p;
long long nz(long long x)
{
    long long rez=0;
    for(long long i=5;i<=x;i*=5)
        rez+=x/i;
    return rez;
}
int main()
{
    fin>>p;
    long long st=1,dr=p*5,mj=0;
    while(st<=dr)
    {
        mj=(st+dr)/2;
        if(nz(mj)<p)
            st=mj+1;
        else
            dr=mj-1;
    }
    if(nz(st)==p)
        fout<<st;
    else
        fout<<"-1";
    return 0;
}