#include <bits/stdc++.h>
using namespace std;
int exp(int l)
{
    int put=5;
    int sum=0;
    while(l>=put)
    {
        sum+=l/put;
        put*=5;
    }
    return sum;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p;
    int st=1,dr=10000000;
    scanf("%d",&p);
    if(p==0)
    {
        printf("1\n");
        return 0;
    }
    while(st<=dr)
    {
        int med=(st+dr)/2;
        int ex1=exp(med);
        if(ex1>p)dr=med-1;
        if(ex1==p)
        {
            printf("%d\n",med/5*5);
            return 0;
        }
        if(ex1<p)st=med+1;
    }
    return 0;
}