#include <cstdio>
int main()
{
	int n,x=0,y,v[]={5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125};
	
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&n);
	y=n*5;

	while (x<=y)
	{
		int nr,i,z=(x+y)/2;
		for (i=nr=0;v[i]<=z;++i)
			nr+=z/v[i];
		if (nr<n)
			x=z+1; else
				if (nr>n) 
					y=z-1; else
		{printf("%d",z/5*5);break;} 
	}
	return 0;}