Untitled

function countSubstringsWithKDistinctLetters(n, k, str) {
    let count = 0;
    let charCount = {};
    let distinctCount = 0;
    
    // Initialize the first window
    for (let i = 0; i < k; i++) {
        if (!charCount[str[i]]) {
            charCount[str[i]] = 0;
        }
        charCount[str[i]]++;
        if (charCount[str[i]] === 1) {
            distinctCount++;
        }
    }
    
    if (distinctCount === k) {
        count++;
    }
    
    // Slide the window across the string
    for (let i = k; i < n; i++) {
        let startChar = str[i - k];
        let endChar = str[i];
        
        // Remove the start character of the previous window
        if (charCount[startChar] === 1) {
            distinctCount--;
        }
        charCount[startChar]--;
        
        // Add the end character of the current window
        if (!charCount[endChar]) {
            charCount[endChar] = 0;
        }
        charCount[endChar]++;
        if (charCount[endChar] === 1) {
            distinctCount++;
        }
        
        if (distinctCount === k) {
            count++;
        }
    }
    
    return count;
}

// Function to read input
function main() {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    
    let input = [];
    
    rl.on('line', (line) => {
        input.push(line);
    });
    
    rl.on('close', () => {
        let [n, k] = input[0].split(' ').map(Number);
        let str = input[1];
        
        let result = countSubstringsWithKDistinctLetters(n, k, str);
        console.log(result);
    });
}

// Call the main function to execute the program
main();