#include <stdio.h>
long p,s,n,i;
FILE *f,*g;


int main()
{ f=fopen ("fact.in","r");
  g=fopen ("fact.out","w");
  fscanf (f,"%ld",&p);
 if (p==0) fprintf (g,"1");
 else
 if (p<0) fprintf (g,"-1");
 else  { s=0; for (i=1;i<=p;i++) {n=n+5;

                     if (s==5) {s=0;
                                n=n-5;}
                                s=s+1; }}

fprintf (g,"%ld",n);
fclose(f);
fclose(g);
    return 0;
}