#include<stdio.h>
int putere(int a){
   int i=1,v=5;
   while(v<a){
	v*=5;
	i++;
   }
   return i-1;
}

int main(){
	FILE *f;
	f=fopen("fact.in","r");
	long p;
	int k;
	fscanf(f,"%ld",&p);
	fclose(f);
	f=fopen("fact.out","w");
	if(p==0)     fprintf(f,"1\n");
	else{
		p=5*p;
		k=putere(p);
		if(k==1) fprintf(f,"%ld",p);
		else{
		  p=p-25*(k-2)-5;
		  fprintf(f,"%ld\n",p);
		}
	}
	fclose(f);
	return 0;
}