#include <stdio.h>

FILE *f=fopen("fact.in","r"),*g=fopen("fact.out","w");
int p,x,n,y;

int main()
{
	fscanf(f,"%d",&p);
	if(p==0)
		{
			fprintf(g,"0");
			return 0;
		}
	n=4*p;
	while(x<p)
		{
			x=0;
			if(n%5==0)
				{
					y=n;
					while(y)
						{
							x+=y/5;
							y/=5;
						}
				}
			n++;
		}
	if(x==p)
		fprintf(g,"%d",n-1);
	else
		fprintf(g,"-1");
    return 0;


}