#include<stdio.h>

long long N,P;

void citire ()
{
	FILE *in = fopen ("fact.in", "rt");
    fscanf (in,"%lld", &P);
    fclose(in);
}

void calcul ()
{
	N=P;
    int x=5;
    for(int i=1;P/x>=1;i++)
    {
    	N-=P/x;
        x*=5;
    }
    N++;
    N*=5;
}

void afisare()
{
	FILE *out = fopen ("fact.out", "wt");
    fprintf(out, "%lld", N);
    fclose(out);
}

int main ()
{
	citire();
    calcul();
    afisare();
    return 0;
}