#include<stdio.h>
#include<iostream.h>
long getz(long x){
 long a=(x/5+x/25);
 return a;
}
int main(void){
 long p,i,n=0;
 FILE *in=fopen("fact.in","rt"),*out=fopen("fact.out","w+");
 fscanf(in,"%ld",&p);
 long l=0,r=100000000,m=(l+r)/2;
 while(l<r){
  m=(l+r)/2;
  if(getz(m)==p) {n=m;break;}
  else if (getz(m)<p) l=m;
  else if (getz(m)>p) r=m;
 }

// if(i==100000) fprintf(out,"%ld",i);
 fprintf(out,"%ld",n-1);
}