#include<fstream.h>
#include<math.h>
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{ long long n,p,st,i,dr,sum,ok,k;
  f>>p;
  f.close();
  ok=1;
  st=1;
  dr=(long long)1<<60+1;
  while(ok){ n=(st+dr)/2;
             sum=0;
             k=5;
             for(i=1;n>=k;i=i+1,k=k*5) sum=sum+n/k;
             if(sum>p) dr=n-1;
               else if(sum<p) st=n+1;
                      else ok=0;
                }
  n=n-n%5;
  g<<n;                 
  g.close();
  return 0;
}