#include<stdio.h>
FILE*f=fopen("fact.in","r");
FILE*g=fopen("fact.out","w");
int P;
int u,m,p,x,nr;
int main () {
	fscanf(f,"%d",&P);
	u=5*P;
	p=1;
	while(p<=u){
		m=p+(u-p)/2;
		x=5;
		nr=0;
		while(x<=m){
			nr+=m/x;
			x*=5;
		}
		if(nr>=P)
			u=m-1;
		else
			p=m+1;
	}
	if(P==1)
		fprintf(g,"0");
	else
		fprintf(g,"%d",p);
	
	fclose(f);
	fclose(g);
	return 0;
}