#include<stdio.h>
int factorial(int n){
	int p=0;
	while(n>0){
		p+=n/5;
		n/=5;
	}
	return p;
}
int main () {
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	int n=0,p,nr=0;
	scanf("%d",&p);
	if(p==0)
		n=1;
	if(p<0)
		n=-1;
	while(nr<p){
		n+=5;
		nr=factorial(n);
	}
	printf("%d",n);
	fclose(stdin);
	fclose(stdout);
	return 0;
}