#include <stdio.h>
int parte(int n)
{
    if(n<5)
        return n;
    if(n==5)
        return -1;
    if(n*5>25)
    {
        int k=25/(n*5)+1;
        return n-k;

    }
}
int main()
{
    int n;
    FILE *f=fopen("fact.in","r");
    fscanf(f,"%d",&n);
    fclose(f);
    FILE *g=fopen("fact.out","w");
    if(n==0)
    {
        fprintf(g,"1");
        return 0;
    }
    fprintf(g,"%d",5*parte(n));
    fclose(g);
    return 0;
}