#include <iostream>
#include <stdio.h>

long long p;
long long nr_cifre0(long long nr)
{
    long long s=0,i;
    for(i=5;i<=nr;i*=5)
    {
        s += nr/i;
    }
    return s;
}
long long func(long long x)
{
    long long i,pas=1LL<<40;
    for(i=0;pas!=0;pas=pas/2)
    {
        if(nr_cifre0(i+pas)<p)
        {
            i+=pas;
        }
    }
    return i+1;
}

int main()
{
    FILE *f=fopen("factorial.in","r");
    FILE *g=fopen("factorial.out","w");
    fscanf(f,"%lld",&p);

    fprintf(g,"%lld",func(p));

    fclose(f);
    fclose(g);
    return 0;
}