#include<cstdio>
/*
	[53/5]+[53/25]=10+2=12 zero-uri;
cautbin cel mai mic "n" cu prop ca "zero(n)>=p";
*/
int p;

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

int cautbin(int a)
{
	int i,pas=1<<26;
	for(i=0;pas!=0;pas/=2)
	{
		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);
	printf("%d\n",cautbin(p));
	return 0;
}