minlex

#include <iostream>
#include <cstring>
#define Nmax 1000001
using namespace std;

int main()
{
    int k;
    char cuv[Nmax],st[Nmax];
    cin>>k>>cuv;
    unsigned int L=strlen(cuv);
    int vf=0;
    for(unsigned int i=0;i<L;++i)
    {
        while(vf&&k&&st[vf]>cuv[i])
            --vf,--k;
        st[++vf]=cuv[i];
    }
    vf-=k;
    st[vf+1]=0;
    cout<<st+1;
    return 0;
}