#include <stdio.h>

int main(){
	FILE *fin,*fout;
	long int P,k;
	long int N,aux;
	
	fin=fopen("fact.in","rt");
	fout=fopen("fact.out","wt");
	
	fscanf(fin,"%ld",&P);
	
	if (P==0){
		N=1;
		fprintf(fout,"%ld",N);
		fclose(fin);
		fclose(fout);
		return 0;
	}
	

	N=P*5;
	
	while(1){
		k=N;
		aux=-1;
		while (k%5==0){
			k/=5;
			aux++;
		}
		
		if (aux>0){
			N-=5;
			continue;
		}
		
		fprintf(fout,"%ld",N);
		fclose(fin);
		fclose(fout);
		return 0;
		
			
	}
	
	
	return 0;
}