#include <iostream>
#include <cstdio>
using namespace std;
FILE *f,*g;
int x,p;
int zero(int n)
{
    int nr = 0;
    while (n >= 5)
    {
        nr += n / 5;
        n /= 5;
    }
    return nr;
}
int cautzero(int p)
{
    int i=0,p5;
    while(p5<p)
    {
        i+=5;
        p5=zero(i);
    }
    return i;
}
int main()
{
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%d",&p);
    x=cautzero(p);
    if(p)
        fprintf(g,"%d",x);
    else fprintf(g,"1");
    fclose(f);
    fclose(g);
    return 0;
}