#include <bits/stdc++.h>

using namespace std;
ifstream in("factorial.in");
ofstream out("factorial.out");

int p;

int fact(int n)
{
    int sum=0;
    int p=5;
    while(n>=p)
    {
        sum+=n/p;
        p*=5;
    }
    return sum;
}

int main(){


    in>>p;
    int st=0,dr=100000005;
    int res=0;
    while(st<=dr)
    {
        int mid=(st+dr)/2;
        if(fact(mid)>p)
        {
            dr=mid-1;
        }
        else if(fact(mid)==p)
        {
            dr=mid-1;
            res=mid;
        }
        else{
            st=mid+1;
        }
    }
    out<<res;


    return 0;
}