#include<stdio.h>

FILE *f=fopen("fact.in","r");
FILE *g=fopen("fact.out","w");

int main()
{
	long i,n=0,p,ok,z;
	fscanf(f,"%ld",&p);
	if(p==0)
	{
		fprintf(g,"1");
		fclose(f);
		fclose(g);
		return 0;
	}
	else 
		for(i=5;p>0;i+=5)
		{
			ok++;
			n+=5;
			for(z=5;z<=ok;z*=5)
				if(ok%z==0)p--;
			p--;
		}
	fprintf(g,"%ld",n);
	
	fclose(f);
	fclose(g);
	
	return 0;
}