#include <bits/stdc++.h>

using namespace std;
int zerouri (int x)
{
    int nr=0, imp=5;
    while(x>=imp)
    {
        nr+=x/imp;
        imp*=5;
    }
    return nr;
}

int factorial(int x)
{
    int rez=1;
    for(int i =2; i<=x;++i)rez*=i;
    return rez;
}

int bs(int left,int right, int val)
{
    int m,poz=-1;
           while(left<=right)
           {
               m=left+(right-left)/2;
               int zero=zerouri(m);
               if(zero==val)
               {
                   poz=m;
               }
               if(zero>=val)
                right=m-1;
               else left=m+1;
           }
           return poz;
}

int main()
{ //cout<<factorial(10)<<" ";
    //cout <<zerouri(10);
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
      int p;
       cin >> p ;
       if(p==0)
        cout<<1;
       else{
         cout<<bs(1,p*5,p);
       }
    return 0;
}