#include<cstdio>

long long p,s,j;
void cit()
{
	scanf("%d",&p);
}

void rez()
{
	s=0;
	int t=0;
	int k,m=0;
	if(p==0)
		j=1;
	else
	while(s<p)
	{
		m+=5;k=0;
		t=m;
		while(t==t/5*5)
		{
			t/=5;
			++k;
		}
		s+=k;
		j+=5;
	}
}


void afis()
{
	printf("%lld",j);
}



int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	
	
	cit();
	rez();
	afis();
	
	return 0;
}