#include <stdio.h>

int main()
{
	FILE* f=fopen("fact.in","r");
	FILE* g=fopen("fact.out","w");
	int n,i,ver,sol,cont;
	
	fscanf(f,"%d", &n);
	fclose(f);
	sol=n*5;
	cont=n;
	for (i=25;i<sol;i+=25){
		ver=25;
		do {
			cont--;
			ver*=5;
		}while (i%ver==0);
	}

	fprintf(g,"%d", n*5-(n-cont)*5);
	fclose(g);
	return 0;
}