#include<math.h>
#include<fstream>
using namespace std;
long long putere(long long x,long long y)
{
	long long c=x;
	for(;y!=1;x*=c,--y);
	return x;
}
long long procedeu(long long n)
{
	long long x=log(n)/log(5),s=0;
	for(;x!=0;s+=(n/putere(5,x)),--x);
	return s;
}
int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	long long p,n;
	f>>p;
	for(n=5*p;procedeu(n)!=p;n-=5);
	g<<n;
	f.close();
	g.close();
}