#include<stdio.h>

int n, aux=5, nr, start=1, end=1000000000, mid;
int p;

int calc(int x)
{
	aux=5;
	nr=0;
	while(x/aux>0)
	{
		nr+=x/aux;
		aux*=5;
	}
	return nr;
}


int main()
{
	freopen("factorial.in", "r", stdin);
	freopen("factorial.out", "w", stdout);
	scanf("%d", &p);
	while(start<end)
	{
		mid=(start+end)/2;
		if(calc(mid)>=p)
			end=mid;
		else start=mid+1;
	}
	printf("%d", start/5*5);	
	return 0;
}