#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE *pf,*fp;
    int p,n,r,i=0,k=1,m,t;
    pf=fopen("fact.in", "r");
    fscanf(pf, "%d", &p);
    fclose(pf);
    m=5*p;
    /*while((k*5)<=m)
    {
        k=k*5;
        i++;
    }
    printf("%d %d %d",k,i,m);*/

    t=m/25;
    r=p-t;
    n=5*r;
    fp=fopen("fact.out", "w");
    fprintf(fp,"%d",n);
    fclose(fp);
   /*while(k>=25)
    {
        t=m/k;
        r=r-(t*(i-1));
        k=k/5;
        i--;
        m=r*5;
        printf("\n%d %d %d",m,r,t);

    }
    n=r*5;
    printf("\n%d", n);*/

}