#include <stdio.h>


#define NMAX 2000
char bits[NMAX];

void solve(void)
{
	FILE *fin, *fout;
	int N, swaps = 0, i, j;

	fin = fopen("swaps2.in", "rt");
	fout = fopen("swaps2.out", "w+");

	fscanf(fin, "%d ", &N);

	// N should be equal with strlen(bits);
	for (i = 0; i < N; i++)
		fscanf(fin, "%c", &bits[i]);
	//forward writing, just to hold space for first line
	//we'll be back to this when swaps will be known
	fprintf(fout, "%d\n", swaps);
	i = 0; j = N - 1;
	//walk the array from both ends, check and count swaps
	// i -> .... <- j
	while (i < j) {
		if (bits[i] == '0') {
			i++;
			continue;
		}
		if (bits[j]=='1') {
			j--;
			continue;
		}
		//at this point we must simulate swap between i <-> j
		fprintf(fout, "%d %d\n", i+1, j+1);
		swaps++;
		i++; j--;
	}

	//go back and write the actual number of swaps
	fseek(fout, 0, SEEK_SET);
	fprintf(fout, "%d\n", swaps);

}


int main(void)
{
	solve();

	return 0;
}