#include <cstdio>

using namespace std;

int zero(int n)
{
	int s=0,p=5;
	while(n>=p)
	{
		s+=n/p;
		n/=p;
	}
	return s;
}

int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);

int p;
scanf("%d",&p);

int nr=0;
int k=5;
int j;

while(nr<p)
{
	nr+=zero(k);
	k+=5;
}

printf("%d",k);

return 0;
}