#include <iostream>
#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long v[19];

long fct(long long &x){
    long k=0;
    for(int i=0;i<=18||x<v[i];i++) k+=x/v[i];
    return k;
}

int main()
{
    long long p,s,d,a;
    v[0]=5;
    for(int i=1;i<=18;i++) v[i]=v[i-1]*5;
    long x;
    f>>p;
    s=0;
    d=p*5;
    while(s<d){
        a=(s+d)/2;
        x=fct(a);
        if(x==p){ g<<a-a%5<<endl; return 0; }
        else if(x>p) d=a-1;
        else s=a+1;
    }
    a=d-5;
    g<<-1<<endl;


    return 0;
}