#include<stdio.h>

int main(void){
    int n,k,time,n1,i;
    scanf("%d%d",&n,&k);
    i=1;
    n1=1;
    time=0;
    while(n1<k && n1<n){
        n1=n1+i;
        i++;
        time++;
    }
    if(n - n1>0){
        if((n-n1) % k == 0)
            time=time+(n-n1)/k;
        else
            time=time+(n-n1)/k+1;
    }
    printf("%d",time);
return 0;
}

Hints:
 1) your while loop condition is not quite right.
2) you are not growing n1 properly in the while loop
3) your "if (n - n1>0)" is not necessary, if n-n1 == 0 then the division result will be zero
4) integer ceiling of x/y can be done in a single step like this: (x + y - 1)/y
5) it's generally a good idea to finish each line of output with a newline character

In general: do some examples on paper, and step through your code in the debugger, or put in a bunch of print statements to follow the progress of the solution, and you'll discover where the problems are.