#include <stdio.h>
int main(void){
    long int N;     //  number of boxes
    long int K;     //  place of trap
    long int count = 0; //  number of cheeses 'r' can eat

    scanf("%ld %ld",&N,&K);

    if(K != 0 && N >= K){
        count = N;
        if(K == N-K+1){
            count--;
        }else{
            count -= 2;
        }
    }

    printf("%ld\n",count);

    return 0;
}