#include<fstream>
using namespace std;
int main()
{ int p,i,g,max=-int(2e9);
ifstream in("fact.in");
ofstream out("fact.out");
in>>p;
if(p==0)
{out<<1<<"\n";
}
else
{
for(i=1;p>=0;i++)
{g=i;
if(i>max)
{max=i;
}
while(g%5==0)
{g=g/5;
p=p-1;
}
}
out<<max-5<<"\n";
}
in.close();
out.close();
return 0;
}