#include <iostream>
#include <fstream>

using namespace std;

long long v[]={5,25,125,625,3125,15625,78125,390625,1953125,9765625};

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

long fct(long long x){
    long k=0;
    for(int i=0;i<10||x<v[i];i++) k+=x/v[i];
    return k;
}

int main()
{
    long long p,s,d,a;
    long x;
    f>>p;
    s=0;
    d=10000;
    while(s<d){
        a=(s+d)/2;
        x=fct(a);
        a=a-a%5;
        if(x>p) d=a;
        else s=a+5;
    }
    if(fct(s-5)==p) g<<s-5;
    else g<<-1;


    return 0;
}