#include<stdio.h>

int main()
{
    FILE *f, *g;

    int n,i;

    f=fopen("fact.in","r");
    g=fopen("fact.out","w");

    fscanf(f,"%d",&n);

    if(n==0)
    {
        fprintf(g,"1\n");
        exit(0);
    }
    else
    {
        i=5;
        while(f0(i)!=n)
            i++;
    }
    fprintf(g,"%d\n",i);

    fclose(f);
    fclose(g);

    return 0;
}
int f0(int fkt)
{
    int div=5,d=0;

    while(div<=fkt)
    {
        d=d+fkt/div;
        div*=5;
    }
    return d;
}