#include<fstream>
int main()
{
   int u,c=0,z=1;
   unsigned long long j,p,i;
   std::ifstream f("fact.in");
   f>>p;f.close();
   i=5*p;
   for(j=25;j<=i;j+=25)
   {u=j;
    while(!(u%5)){u/=5;c++;}
    c--;}
    while(i>25&&i%25)i--;
   for(j=i;j>=25&&c;j-=25)
   {u=j;
    while(!(u%5)){u/=5;c--;}
    c++;if(c)i-=5;}
   std::ofstream g("fact.out");
   if(!p)g<<1;
   else g<<i;g.close();
}