#include<stdio.h>
int a[100000],b[100000];
int main () {
    FILE *fin, *fout;
    int n,i,j,max,s;
    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];
    }
    s=0;
    i=1;
    while(i<=max) {
        for(j=0;j<n;j++) {
            if(a[j]==i) {
                s=s+(b[j]-a[j]);
                i=i+(b[j]-a[j]);
            }
        }
        if(j==n)
        i++;
    }
    fclose(fin);
    fout=fopen("heavymetal.out","w");
    fprintf(fout,"%d",s);
    fclose(fout);
    return 0;
}