#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long  e,min1=1,max1=1000000000,mid,f;
int fct()
{
    mid=(min1+max1)/2;
    for(int i=5;i<=mid;i*=5)
    {
        e+=(mid/i);
    }
    if(e<f)
    {
        min1=mid+1;
    }
    else
    {
        max1=mid;
    }
}
int main()
{
    fin>>f;
    while(min1!=max1)
    {
        fct();
        e=0;
    }
    mid=(min1+max1)/2;
    for(int i=5;i<=mid;i*=5)
    {
        e+=(mid/i);
    }
    if(e<f)
    {
        min1=mid+1;
    }
    else
    {
        max1=mid;
    }
    if(e==f)
        fout<<min1;
    else
        fout<<"-1";
}