#include <stdio.h>

int main()
{
	long long s,m;
	long a=0,b=500,x=250,p;
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%ld",&p);
	while(a<b-1){
		s=0;
		m=5;
		while(m<=x){
			s=s+x/m;
			m=m*5;
		}
		//printf("%lld ",s);
		if(s>p){
			b=x;
			//printf(" 1 ");
			x=(a+b)/2;
		}
		if(s<p){
			a=x;
			//printf("1 ");
			x=(a+b)/2;
		}
		if(s==p){
			break;
		}
	}
	printf("%ld",x-x%5);
	return 0;
}