#include <iostream>
#include <fstream>
std::ifstream fin("fact.in");
std::ofstream fout("fact.out");

int zeros(unsigned long long n)
{
    int s=0, p=5;
    while(n/p)
    {
        s+=n/p;
        p*=5;
    }
    return s;
}
int main(int argc, char *argv[])
{
    int p;
    fin>>p;
    if(p==0) fout<<1;
    else
    {
        int s=5,d=400000015;
        int n;
        while(s<d)
        {
            n=(s+d)/2;
            if(zeros(n)<p) s=n+1;
            else d=n;
        }
        n-=n%5;
        fout<<n;
    }

    return 0;
}