#include<stdio.h>

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

int caut(int p)
{
	int i,pas=1<<26;
	for(i=0;pas!=0;pas=pas/2)
	{
		if(zero(i+pas)<p)
			i+=pas;
	}
	return 1+i;
}

int main()
{
	int n,p;
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&p);
	n = caut(p);
	printf("%d",n);
	return 0;
}