#include <stdio.h>
#include <math.h>

FILE*f = fopen("fact.in","r");
FILE*g = fopen("fact.out","w");

int v[100002];
int i,s,j,x,p,u,m;

int main() {
	
	for (i=1;i<=100001;i++) {
		j=1;
		s=0;
		while (i/int(pow(5,j)) > 0){
			s+=i/int(pow(5,j));
			j++;
		}
		v[i]=s;
	}
	//printf("%d",v[100000]);
	
	fscanf(f,"%d",&x);
	
	p=1; u=100002;
	while (p<=u){
		m = p + (u-p)/2;
		if(v[m]>=x)
			u=m-1;
		else
			p=m+1;
	}
	fprintf(g,"%d\n",p);

	return 0;
}