#include <fstream>
#include <vector>

using namespace std;

ifstream cin("fact.in");
ofstream cout("fact.out");

int p;

void read() {
    cin>>p;
}

int verify(int nr) {
    int cnt=nr/5;
    for(int i=5*5;i<=nr;i*=5) {
        cnt+=nr/i;
    }
    return cnt;
}

int bs() {
    int l=1,r=1e9,mid,res=-1;
    while(l<=r) {
        mid=l+(r-l)/2;
        if(verify(mid)>=p) {
            res=mid;
            r=mid-1;
        }
        else {
            l=mid+1;
        }
    }
    return res;
}

void solve() {
    cout<<bs();
}

int main() {
 
    read();
    solve();
    return 0;
}