#include <stdio.h>

int main(void) {
    long long int i, P, N, K, win, lose, turn;
    scanf("%lld", &P);
    turn = 1;
    win = 0;
    lose = 0;
    for(i = 0;i < P;i++){
        scanf("%lld%lld", &N, &K);
        if(N % (K + 1) == 1){
            if(turn == 1)turn = 0;
            else turn = 1;
        }
        else{
            if(turn == 1)win++;
        }
    }
    printf("%lld\n", win);

    return 0;
}