#include <fstream>
#include<iostream>
using namespace std;
int main()
{
    ifstream in;in.open("fact.in");
    ofstream ou;ou.open("fact.out",ofstream::out);
    long n,i,r,q,j;
    q=0;r=5;j=0;
    in>>n;
    if(n==0)ou<<1;
    else
    for(i=5;;i+=5)
        {
        q+=1;
        if(i==r){q+=j;j+=1;r*=r;}
        if(q==n){ou<<i;break;}
        else if(q>n){ou<<-1;break;}
        }
    in.close();ou.close();
    return 0;
}