#include<stdio.h>
int P,p,x,nr;
FILE *in=fopen("fact.in","rt"),*out=fopen("fact.out","wt");
int main()
{
	fscanf(in,"%d",&P);
	fclose(in);
	while(p!=P)
	{
		nr+=5;
		x=nr;
		if(p!=P)
		{
				while(x%5==0)
				{
					p++;
					x/=5;
				}
		}
		else
			break;
	}
	if(P==0)
        fprintf(out,"1");
    else
      if(P!=p)
       fprintf(out,"-1");
     else
        fprintf(out,"%d",nr-5);
        fclose(out);
	return 0;
}