#include<fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
long long p,rez = -1;
int main()
{
    cin >> p;
    long long st = 1,mid,dr = 1000000100,aux1;
    while(st <= dr)
    {
        mid = st + dr;mid/=2;
        aux1 = 0;
         
        for(int i = 5; i <= mid; i *= 5)aux1+=(mid/i);
        if (aux1 == p) rez = mid, dr = mid-1;
        else if (aux1 > p)
        {
            dr = mid - 1;
        }else st = mid + 1;
    }
    //if (rez == 100000010) cout << "-1";
    cout << rez;
}