#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int P,i;
int verificare(int x){
    int k,i,p;
    p=5;
    k=0;
    while (x/p>0){
       k=k+x/p;
       p=p*5;
    }
    return k;
}
int main(){
   fin>>P;
   fin.close();
   if (P==0) {fout<<"1";
              fout.close();
              return 0;}
   i=5;
   while(P!=verificare(i))
     i=i+5;
   fout<<i;
   fout.close();
   return 0;
}