#include<stdio.h>
int a[100000],b[100000];
int main () {
    FILE *fin, *fout;
    int n,i,j,max,s,st;
    fin=fopen("heavymetal.in","r");
    fscanf(fin,"%d",&n);
    max=1;
    for(i=0;i<n;i++) {
    fscanf(fin,"%d%d",&a[i],&b[i]);
    if(b[i]>max)
    max=b[i];
    }
    //printf("max = %d  ",max);
    s=0;
    i=1;
    while(i<max) {
        st=0;
        for(j=0;j<n;j++) {

            if(a[j]==i) {
        //while(j<n && a[j]==i) {
                //printf("%d %d ",a[j],b[j]);
                s=s+(b[j]-a[j]);
                //printf("%d\n  ",s);
                i=b[j];
                st++;
            }
        }
        if(st==0)
        i++;
    }
    fclose(fin);
    fout=fopen("heavymetal.out","w");
    fprintf(fout,"%d",s);
    fclose(fout);
    return 0;
}