#include<cstdio>
const int N=1<<9;
int p;
int zero (int n)
{ 
	int s=0;
	while (n);
	{
		s+=n/5;
		n/=5;
	}
	return s;
}

int fact(int p)
{
	int i,pas=N;
	for ( i=0; pas;pas>>=1)
    if (zero(i+pas)<p)
		i+=pas;
	return (i+1);
}
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&p);
	int k=fact(p);
	printf("%d",k);
	return 0;
}