codeforce499A - Watching a movie

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>

using namespace std;
const int maxn = 100;
int n,x;
struct node{
int l,r;
}c[maxn];
int main()
{
   scanf("%d %d",&n,&x);
    for(int i=0; i<n; i++)
        scanf("%d %d",&c[i].l,&c[i].r);
        int st=1,sum=0;
    for(int i=0; i<n ;i++)
    {
        sum+=(c[i].l-((c[i].l-st)/x*x+st))+(c[i].r-c[i].l+1);
//        printf("%d\n",sum);
        st=c[i].r+1;
    }
    printf("%d\n",sum);
    return 0;
}