#include<stdio.h>
FILE *f=fopen("fact.in","r");
FILE *g=fopen("fact.out","w");
long p,n,s,nr;
int i;
int main()
{
fscanf(f,"%d",&p);
if(p==0) n=1;
else{ n=0;
      for(i=1;i<p&&n<p;i++) {  nr+=5;
                                s=nr;
                                for(s=n;s>4;++s) if(s%5==0){ s/=5;n++;}
                             }

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