#include<stdio.h>
FILE *f=fopen("factorial.in","r");
FILE *g=fopen("factorial.out","w");
long p,n,s,nr;
int main()
{
fscanf(f,"%d",&p);
if(p==0) n=1;
else{ n=0;
      while(n<p) { nr+=5;
                    s=nr;
                    while(s%5==0){ s/=5;n++;}
                 }

      n=nr;
    }
fprintf(g,"%d",n);
fclose(f);
fclose(g);
return 0;
}