#include<cstdio>
using namespace std;

const long long NMAX=10e8*5;

long long putere(long long nr){
    long long p5=5,s=0;
    while(p5<=nr){
        s+=nr/p5;
        p5*=5;
    }
    return s;
}

long long bs(long long st, long long dr, long long val){
    long long sol=-1;
    while(st<=dr){
        long long mij=(st+dr)/2;
        if(putere(mij)>=val)
            dr=mij-1,sol=mij;
        else
            st=mij+1;
    }
    return sol;
}

int main(){
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p;
    scanf("%d", &p);
    printf("%lld", bs(1, NMAX, p));
    return 0;
}