Javascript (Node.js) solution:

let pageno = 1, result = 0;

for(let i=0;i<n;i++) {
    let x = arr[i], j=1, y = x-k;
    while(y>=-(k-1)) {
        let lwr = k*(j-1), upr = k* j;
        if(pageno>lwr && pageno<=upr && pageno<=x)
            result++;
        j++;
        y-=k;
        pageno++;
    }
}

return result;