#include <bits/stdc++.h>
#define PMAX 21000000000
#define LL long long int

using namespace std;

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

LL n;

LL nz(LL x){
  LL p = 5 , rez = 0;
  while(p <= x)
  {
    rez += x/p;
    p = p * 5;
  }
  return rez;
}

LL cb(){
    LL st = 1 , dr = PMAX , mij = 0 , mini = -1;
    while(st <= dr)
    {
        mij = st + (dr - st) / 2;
        if(nz(mij) >= n)
        {
            mini = mij;
            dr = mij - 1;
        }
        else st = mij + 1;
    }
    return mini;
}

int main()
{
    f>>n;
    g<<cb();
    return 0;
}